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Chen JT, Kan NW, Barquero C, Teo MMJ, Wang CA. Saccade Latency and Metrics in the Interleaved Pro- and Anti-Saccade Task in Open Skill Sports Athletes. Scand J Med Sci Sports 2024; 34:e14713. [PMID: 39155402 DOI: 10.1111/sms.14713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Revised: 06/17/2024] [Accepted: 07/29/2024] [Indexed: 08/20/2024]
Abstract
Evidence has demonstrated that athletes exhibit superior cognitive performance associated with executive control. In the oculomotor system, this function has been examined using the interleaved pro-saccade and anti-saccade task (IPAST), wherein participants, prior to target appearance, are instructed to either automatically look at the peripheral target (pro-saccade) or suppress the automatic response and voluntarily look in the opposite direction (anti-saccade). While the IPAST has provided much insight into sensorimotor and inhibitory processing, it has yet to be performed in athletes. Moreover, limited research has examined saccade metrics in athletes. Here, we examined saccade latency and movement kinematics in the IPAST among athletes (N = 40) and nonathletes (NON) (N = 40). Higher direction error rates were obtained in the anti-saccade compared to the pro-saccade condition, with no differences between athletes and NON noted. Significantly faster saccade latencies were observed in athletes compared to NON in both conditions, in addition to faster pro-saccades compared to anti-saccades. Furthermore, athletes showed significantly higher frequencies and faster latencies of express saccades compared to NON in correct pro-saccades. Additionally, athletes exhibited significantly faster latencies of express saccades compared to NON in erroneous anti-saccades. Differences in saccade metrics between athletes and NON were not seen. Overall, these findings demonstrate that athletes display altered saccade performance likely associated with sensorimotor and preparatory processing, highlighting the potential of using IPAST to objectively investigate sensorimotor and cognitive functions in athletes.
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Affiliation(s)
- Jui-Tai Chen
- Department of Anesthesiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei City, Taiwan
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
| | - Nai-Wen Kan
- Center of General Education, Taipei Medical University, Taipei City, Taiwan
| | - Cesar Barquero
- Department of Physical Activity and Sport Science, Universidad Peruana de Ciencias Aplicadas, Lima, Peru
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City, Taiwan
| | - Moeka Mong Jia Teo
- Graduate Institute of Injury Prevention and Control, Taipei Medical University, Taipei City, Taiwan
| | - Chin-An Wang
- Department of Anesthesiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei City, Taiwan
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Eye-Tracking Laboratory, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
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2
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Caziot B, Cooper B, Harwood MR, McPeek RM. Physiological correlates of a simple saccadic-decision task to extended objects in superior colliculus. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.09.584223. [PMID: 38559019 PMCID: PMC10979857 DOI: 10.1101/2024.03.09.584223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Our vision is best only in the center of our gaze, and we use saccadic eye movements to direct gaze to objects and features of interest. We make more than 180,000 saccades per day, and accurate and efficient saccades are crucial for most visuo-motor tasks. Saccades are typically studied using small point stimuli, despite the fact that most real-world visual scenes are composed of extended objects. Recent studies in humans have shown that the initiation latency of saccades is strongly dependent on the size of the target (the "size-latency effect"), perhaps reflecting a tradeoff between the cost of making a saccade to a target and the expected information gain that would result. Here, we investigate the neuronal correlates of the size-latency effect in the macaque superior colliculus. We analyzed the latency variations of saccades to different size targets within a stochastic accumulator model framework. The model predicted a steeper increase in activity for smaller targets compared to larger ones. Surprisingly, the model also predicted an increase in saccade initiation threshold for larger targets. We found that the activity of intermediate-layer SC visuomotor neurons is in close agreement with the model predictions. We also found evidence that these effects may be a consequence of the visual responses of SC neurons to targets of different sizes. These results shed new light on the sources of delay within the saccadic system, a system that we heavily depend upon in the performance of most visuo-motor tasks.
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Affiliation(s)
- B. Caziot
- Graduate Center for Vision Research, Department of Biological and Vision Sciences, SUNY College of Optometry, 33 West 42 Street, New York, NY, 10036, USA
- Neurophysics Department, Philipps-Universität Marburg, 8A Karl-von-Frisch-Straße, 35043 Marburg, Germany
- Center for Mind, Brain and Behavior (CMBB), Philipps-Universität Marburg and Justus–Liebig–Universität Gießen, Gießen, Germany
| | - B. Cooper
- Graduate Center for Vision Research, Department of Biological and Vision Sciences, SUNY College of Optometry, 33 West 42 Street, New York, NY, 10036, USA
| | - M. R. Harwood
- Department of Psychological Sciences, University of East London, London, UK
| | - R. M. McPeek
- Graduate Center for Vision Research, Department of Biological and Vision Sciences, SUNY College of Optometry, 33 West 42 Street, New York, NY, 10036, USA
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Wang CA, Muggleton NG, Chang YH, Barquero C, Kuo YC. Time-on-task effects on human pupillary and saccadic metrics after theta burst transcranial magnetic stimulation over the frontal eye field. IBRO Neurosci Rep 2023; 15:364-375. [PMID: 38046886 PMCID: PMC10689284 DOI: 10.1016/j.ibneur.2023.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 10/01/2023] [Accepted: 11/01/2023] [Indexed: 12/05/2023] Open
Abstract
Pupil size undergoes constant changes primarily influenced by ambient luminance. These changes are referred to as the pupillary light reflex (PLR), where the pupil transiently constricts in response to light. PLR kinematics provides valuable insights into autonomic nervous system function and have significant clinical applications. Recent research indicates that attention plays a role in modulating the PLR, and the circuit involving the frontal eye field (FEF) and superior colliculus is causally involved in controlling this pupillary modulation. However, there is limited research exploring the role of the human FEF in these pupillary responses, and its impact on PLR metrics remains unexplored. Additionally, although the protocol of continuous theta-burst stimulation (cTBS) is well-established, the period of disruption after cTBS is yet to be examined in pupillary responses. Our study aimed to investigate the effects of FEF cTBS on pupillary and saccadic metrics in relation to time spent performing a task (referred to as time-on-task). We presented a bright stimulus to induce the PLR in visual- and memory-delay saccade tasks following cTBS over the right FEF or vertex. FEF cTBS, compared to vertex cTBS, resulted in decreased baseline pupil size, peak constriction velocities, and amplitude. Furthermore, the time-on-task effects on baseline pupil size, peak amplitude, and peak time differed between the two stimulation conditions. In contrast, the time-on-task effects on saccadic metrics were less pronounced between the two conditions. In summary, our study provides the first evidence that FEF cTBS affects human PLR metrics and that these effects are modulated by time-on-task.
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Affiliation(s)
- Chin-An Wang
- Department of Anesthesiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei City, Taiwan
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Eye-Tracking Laboratory, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
| | - Neil G. Muggleton
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City, Taiwan
- Cognitive Intelligence and Precision Healthcare Center, National Central University, Taoyuan City, Taiwan
| | - Yi-Hsuan Chang
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City, Taiwan
| | - Cesar Barquero
- Eye-Tracking Laboratory, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City, Taiwan
- Department of Physical Activity and Sport Science, Universidad Peruana de Ciencias Aplicadas, Lima, Peru
| | - Ying-Chun Kuo
- Department of Anesthesiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei City, Taiwan
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
- Eye-Tracking Laboratory, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan
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Takahashi M, Veale R. Pathways for Naturalistic Looking Behavior in Primate I: Behavioral Characteristics and Brainstem Circuits. Neuroscience 2023; 532:133-163. [PMID: 37776945 DOI: 10.1016/j.neuroscience.2023.09.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 09/09/2023] [Accepted: 09/18/2023] [Indexed: 10/02/2023]
Abstract
Organisms control their visual worlds by moving their eyes, heads, and bodies. This control of "gaze" or "looking" is key to survival and intelligence, but our investigation of the underlying neural mechanisms in natural conditions is hindered by technical limitations. Recent advances have enabled measurement of both brain and behavior in freely moving animals in complex environments, expanding on historical head-fixed laboratory investigations. We juxtapose looking behavior as traditionally measured in the laboratory against looking behavior in naturalistic conditions, finding that behavior changes when animals are free to move or when stimuli have depth or sound. We specifically focus on the brainstem circuits driving gaze shifts and gaze stabilization. The overarching goal of this review is to reconcile historical understanding of the differential neural circuits for different "classes" of gaze shift with two inconvenient truths. (1) "classes" of gaze behavior are artificial. (2) The neural circuits historically identified to control each "class" of behavior do not operate in isolation during natural behavior. Instead, multiple pathways combine adaptively and non-linearly depending on individual experience. While the neural circuits for reflexive and voluntary gaze behaviors traverse somewhat independent brainstem and spinal cord circuits, both can be modulated by feedback, meaning that most gaze behaviors are learned rather than hardcoded. Despite this flexibility, there are broadly enumerable neural pathways commonly adopted among primate gaze systems. Parallel pathways which carry simultaneous evolutionary and homeostatic drives converge in superior colliculus, a layered midbrain structure which integrates and relays these volitional signals to brainstem gaze-control circuits.
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Affiliation(s)
- Mayu Takahashi
- Department of Systems Neurophysiology, Graduate School of Medical and Dental, Sciences, Tokyo Medical and Dental University, Japan.
| | - Richard Veale
- Department of Neurobiology, Graduate School of Medicine, Kyoto University, Japan
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Hsu TY, Wang HY, Chen JT, Wang CA. Investigating the role of human frontal eye field in the pupil light reflex modulation by saccade planning and working memory. Front Hum Neurosci 2022; 16:1044893. [DOI: 10.3389/fnhum.2022.1044893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 11/02/2022] [Indexed: 11/18/2022] Open
Abstract
The pupil constricts in response to an increase in global luminance level, commonly referred to as the pupil light reflex. Recent research has shown that these reflex responses are modulated by high-level cognition. There is larger pupil constriction evoked by a bright stimulus when the stimulus location spatially overlaps with the locus of attention, and these effects have been extended to saccade planning and working memory (here referred to as pupil local-luminance modulation). Although research in monkeys has further elucidated a central role of the frontal eye field (FEF) and superior colliculus in the pupil local-luminance modulation, their roles remain to be established in humans. Through applying continuous theta-burst transcranial magnetic stimulation over the right FEF (and vertex) to inhibit its activity, we investigated the role of the FEF in human pupil local-luminance responses. Pupil light reflex responses were transiently evoked by a bright patch stimulus presented during the delay period in the visual- and memory-delay tasks. In the visual-delay task, larger pupil constriction was observed when the patch location was spatially aligned with the target location in both stimulation conditions. More interestingly, after FEF stimulation, larger pupil constriction was obtained when the patch was presented in the contralateral, compared to the ipsilateral visual field of the stimulation. In contrast, FEF stimulation effects were absence in the memory-delay task. Linear mixed model results further found that stimulation condition, patch location consistency, and visual field significantly modulated observed pupil constriction responses. Together, our results constitute the first evidence of FEF modulation in human pupil local-luminance responses.
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Chen JT, Kuo YC, Hsu TY, Wang CA. Fatigue and Arousal Modulations Revealed by Saccade and Pupil Dynamics. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph19159234. [PMID: 35954585 PMCID: PMC9367726 DOI: 10.3390/ijerph19159234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 07/25/2022] [Accepted: 07/27/2022] [Indexed: 11/16/2022]
Abstract
Saccadic eye movements are directed to the objects of interests and enable high-resolution visual images in the exploration of the visual world. There is a trial-to-trial variation in saccade dynamics even in a simple task, possibly attributed to arousal fluctuations. Previous studies have showed that an increase of fatigue level over time, also known as time-on-task, can be revealed by saccade peak velocity. In addition, pupil size, controlled by the autonomic nervous system, has long been used as an arousal index. However, limited research has been done with regards to the relation between pupil size and saccade behavior in the context of trial-to-trial variation. To investigate fatigue and arousal effects on saccadic and pupillary responses, we used bright and emotional stimuli to evoke pupillary responses in tasks requiring reactive and voluntary saccade generation. Decreased voluntary saccade peak velocities, reduced tonic pupil size and phasic pupillary responses were observed as time-on-task increased. Moreover, tonic pupil size affected saccade latency and dynamics, with steeper saccade main sequence slope as tonic pupil size increased. In summary, saccade dynamics and tonic pupil size were sensitive to fatigue and arousal level, together providing valuable information for the understanding of human behavior.
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Affiliation(s)
- Jui-Tai Chen
- Department of Anesthesiology, School of Medicine, College of Medicine, Taipei Medical University, Taipei 110, Taiwan;
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City 235, Taiwan
| | - Ying-Chun Kuo
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City 320, Taiwan;
- Cognitive Intelligence and Precision Healthcare Research Center, National Central University, Taoyuan City 320, Taiwan
| | - Tzu-Yu Hsu
- Graduate Institute of Mind, Brain, and Consciousness (GIMBC), Taipei Medical University, Taipei 110, Taiwan;
- Brain and Consciousness Research Center (BCRC), TMU-Shuang Ho Hospital, New Taipei City 235, Taiwan
| | - Chin-An Wang
- Department of Anesthesiology, Shuang Ho Hospital, Taipei Medical University, New Taipei City 235, Taiwan
- Institute of Cognitive Neuroscience, College of Health Science and Technology, National Central University, Taoyuan City 320, Taiwan;
- Cognitive Intelligence and Precision Healthcare Research Center, National Central University, Taoyuan City 320, Taiwan
- Graduate Institute of Mind, Brain, and Consciousness (GIMBC), Taipei Medical University, Taipei 110, Taiwan;
- Brain and Consciousness Research Center (BCRC), TMU-Shuang Ho Hospital, New Taipei City 235, Taiwan
- Correspondence:
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7
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Wang CA, White B, Munoz DP. Pupil-linked Arousal Signals in the Midbrain Superior Colliculus. J Cogn Neurosci 2022; 34:1340-1354. [PMID: 35579984 DOI: 10.1162/jocn_a_01863] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
The orienting response evoked by the appearance of a salient stimulus is modulated by arousal; however, neural underpinnings for the interplay between orienting and arousal are not well understood. The superior colliculus (SC), causally involved in multiple components of the orienting response including gaze and attention shifts, receives not only multisensory and cognitive inputs but also arousal-regulated inputs from various cortical and subcortical structures. To investigate the impact of moment-by-moment fluctuations in arousal on orienting saccade responses, we used microstimulation of the monkey SC to trigger saccade responses, and we used pupil size and velocity to index the level of arousal at stimulation onset because these measures correlate with changes in brain states and locus coeruleus activity. Saccades induced by SC microstimulation correlated with prestimulation pupil velocity, with higher pupil velocities on trials without evoked saccades than with evoked saccades. In contrast, prestimulation absolute pupil size did not correlate with saccade behavior. However, pupil velocity correlated with evoked saccade latency and metrics. Together, our results demonstrated that small fluctuations in arousal, indexed by pupil velocity, can modulate the saccade response evoked by SC microstimulation in awake behaving monkeys.
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Affiliation(s)
| | - Brian White
- Queen's University, Kingston, Ontario, Canada
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8
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McPeek RM. Motor control: Ready, steady, go! Curr Biol 2022; 32:R290-R292. [PMID: 35349819 DOI: 10.1016/j.cub.2022.02.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neurons governing saccadic eye movements typically multiplex sensory, cognitive, and movement-related signals. How is a reliable 'go' signal extracted from this mixture? A new study reveals that saccade initiation is gated by the temporal stability of rising population activity.
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Affiliation(s)
- Robert M McPeek
- Department of Biological and Vision Sciences, State University of New York College of Optometry, New York, NY 10036, USA.
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9
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Jagadisan UK, Gandhi NJ. Population temporal structure supplements the rate code during sensorimotor transformations. Curr Biol 2022; 32:1010-1025.e9. [PMID: 35114097 PMCID: PMC8930729 DOI: 10.1016/j.cub.2022.01.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 11/02/2021] [Accepted: 01/06/2022] [Indexed: 10/19/2022]
Abstract
Sensorimotor transformations are mediated by premotor brain networks where individual neurons represent sensory, cognitive, and movement-related information. Such multiplexing poses a conundrum-how does a decoder know precisely when to initiate a movement if its inputs are active at times when a movement is not desired (e.g., in response to sensory stimulation)? Here, we propose a novel hypothesis: movement is triggered not only by an increase in firing rate but, critically, also by a reliable temporal pattern in the population response. Laminar recordings in the macaque superior colliculus (SC), a midbrain hub of orienting control, and pseudo-population analyses in SC and cortical frontal eye fields (FEFs) corroborated this hypothesis. Specifically, using a measure that captures the fidelity of the population code-here called temporal stability-we show that the temporal structure fluctuates during the visual response but becomes increasingly stable during the movement command. Importantly, we used spatiotemporally patterned microstimulation to causally test the contribution of population temporal stability in gating movement initiation and found that stable stimulation patterns were more likely to evoke a movement. Finally, a spiking neuron model was able to discriminate between stable and unstable input patterns, providing a putative biophysical mechanism for decoding temporal structure. These findings offer new insights into the long-standing debate on motor preparation and generation by situating the movement gating signal in temporal features of activity in shared neural substrates, and they highlight the importance of short-term population history in neuronal communication and behavior.
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Affiliation(s)
- Uday K Jagadisan
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260, USA; Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260, USA.
| | - Neeraj J Gandhi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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10
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Schall JD, Paré M. The unknown but knowable relationship between Presaccadic Accumulation of activity and Saccade initiation. J Comput Neurosci 2021; 49:213-228. [PMID: 33712942 DOI: 10.1007/s10827-021-00784-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 01/06/2021] [Accepted: 02/16/2021] [Indexed: 12/01/2022]
Abstract
The goal of this short review is to call attention to a yawning gap of knowledge that separates two processes essential for saccade production. On the one hand, knowledge about the saccade generation circuitry within the brainstem is detailed and precise - push-pull interactions between gaze-shifting and gaze-holding processes control the time of saccade initiation, which begins when omnipause neurons are inhibited and brainstem burst neurons are excited. On the other hand, knowledge about the cortical and subcortical premotor circuitry accomplishing saccade initiation has crystalized around the concept of stochastic accumulation - the accumulating activity of saccade neurons reaching a fixed value triggers a saccade. Here is the gap: we do not know how the reaching of a threshold by premotor neurons causes the critical pause and burst of brainstem neurons that initiates saccades. Why this problem matters and how it can be addressed will be discussed. Closing the gap would unify two rich but curiously disconnected empirical and theoretical domains.
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Affiliation(s)
- Jeffrey D Schall
- Centre for Vision Research, Vision Science to Application, Department of Biology, York University, Ontario, M3J 1P3, Toronto, Canada.
| | - Martin Paré
- Department of Biomedical & Molecular Sciences and of Psychology, Queen's University, Ontario, ON K7L 3N6, Kingston, Canada
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11
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Massot C, Jagadisan UK, Gandhi NJ. Sensorimotor transformation elicits systematic patterns of activity along the dorsoventral extent of the superior colliculus in the macaque monkey. Commun Biol 2019; 2:287. [PMID: 31396567 PMCID: PMC6677725 DOI: 10.1038/s42003-019-0527-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 06/27/2019] [Indexed: 12/21/2022] Open
Abstract
The superior colliculus (SC) is an excellent substrate to study sensorimotor transformations. To date, the spatial and temporal properties of population activity along its dorsoventral axis have been inferred from single electrode studies. Here, we recorded SC population activity in non-human primates using a linear multi-contact array during delayed saccade tasks. We show that during the visual epoch, information appeared first in dorsal layers and systematically later in ventral layers. During the delay period, the laminar organization of low-spiking rate activity matched that of the visual epoch. During the pre-saccadic epoch, spiking activity emerged first in a more ventral layer, ~ 100 ms before saccade onset. This buildup of activity appeared later on nearby neurons situated both dorsally and ventrally, culminating in a synchronous burst across the dorsoventral axis, ~ 28 ms before saccade onset. Collectively, these results reveal a principled spatiotemporal organization of SC population activity underlying sensorimotor transformation for the control of gaze.
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Affiliation(s)
- Corentin Massot
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260 USA
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260 USA
| | - Uday K. Jagadisan
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260 USA
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260 USA
| | - Neeraj J. Gandhi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260 USA
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260 USA
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260 USA
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12
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Smalianchuk I, Jagadisan UK, Gandhi NJ. Instantaneous Midbrain Control of Saccade Velocity. J Neurosci 2018; 38:10156-10167. [PMID: 30291204 PMCID: PMC6246878 DOI: 10.1523/jneurosci.0962-18.2018] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 09/18/2018] [Accepted: 09/22/2018] [Indexed: 01/19/2023] Open
Abstract
The ability to interact with our environment requires the brain to transform spatially represented sensory signals into temporally encoded motor commands for appropriate control of the relevant effectors. For visually guided eye movements, or saccades, the superior colliculus (SC) is assumed to be the final stage of spatial representation, and instantaneous control of the movement is achieved through a rate code representation in the lower brain stem. We investigated whether SC activity in nonhuman primates (Macaca mulatta, 2 male and 1 female) also uses a dynamic rate code, in addition to the spatial representation. Noting that the kinematics of amplitude-matched movements exhibit trial-to-trial variability, we regressed instantaneous SC activity with instantaneous eye velocity and found a robust correlation throughout saccade duration. Peak correlation was tightly linked to time of peak velocity, the optimal efferent delay between SC activity and eye velocity was constant at ∼12 ms both at onset and during the saccade, and SC neurons with higher firing rates exhibited stronger correlations. Moreover, the strong correlative relationship and constant efferent delay observation were preserved when eye movement profiles were substantially altered by a blink-induced perturbation. These results indicate that the rate code of individual SC neurons can control instantaneous eye velocity and argue against a serial process of spatial-to-temporal transformation. They also motivated us to consider a new framework of saccade control that does not incorporate traditionally accepted elements, such as the comparator and resettable integrator, whose neural correlates have remained elusive.SIGNIFICANCE STATEMENT All movements exhibit time-varying features that are under instantaneous control of the innervating neural command. At what stage in the brain is dynamical control present? It is well known that, in the skeletomotor system, neurons in the motor cortex use dynamical control. In the oculomotor system, in contrast, instantaneous velocity control of saccadic eye movements is not thought to be enforced until the lower brainstem. Using correlations between residual signals across trials, we show that instantaneous control of saccade velocity is present earlier in the visuo-oculomotor neuraxis, at the level of superior colliculus. The results require us to consider alternate frameworks of the neural control of saccades.
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Affiliation(s)
- Ivan Smalianchuk
- Department of Bioengineering
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Uday K Jagadisan
- Department of Bioengineering
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
| | - Neeraj J Gandhi
- Department of Bioengineering,
- Department of Neuroscience, and
- Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
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13
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Gu C, Pruszynski JA, Gribble PL, Corneil BD. Done in 100 ms: path-dependent visuomotor transformation in the human upper limb. J Neurophysiol 2017; 119:1319-1328. [PMID: 29212925 DOI: 10.1152/jn.00839.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A core assumption underlying mental chronometry is that more complex tasks increase cortical processing, prolonging reaction times. In this study we show that increases in task complexity alter the magnitude, rather than the latency, of the output for a circuit that rapidly transforms visual information into motor actions. We quantified visual stimulus-locked responses (SLRs), which are changes in upper limb muscle recruitment that evolve at a fixed latency ~100 ms after novel visual stimulus onset. First, we studied the underlying reference frame of the SLR by dissociating the initial eye and hand position. Despite its quick latency, we found that the SLR was expressed in a hand-centric reference frame, suggesting that the circuit mediating the SLR integrated retinotopic visual information with body configuration. Next, we studied the influence of planned movement trajectory, requiring participants to prepare and generate either curved or straight reaches in the presence of obstacles to attain the same visual stimulus location. We found that SLR magnitude was influenced by the planned movement trajectory to the same visual stimulus. On the basis of these results, we suggest that the circuit mediating the SLR lies in parallel to other well-studied corticospinal pathways. Although the fixed latency of the SLR precludes extensive cortical processing, inputs conveying information relating to task complexity, such as body configuration and planned movement trajectory, can preset nodes within the circuit underlying the SLR to modulate its magnitude. NEW & NOTEWORTHY We studied stimulus-locked responses (SLRs), which are changes in human upper limb muscle recruitment that evolve at a fixed latency ~100 ms after novel visual stimulus onset. We showed that despite its quick latency, the circuitry mediating the SLR transformed a retinotopic visual signal into a hand-centric motor command that is modulated by the planned movement trajectory. We suggest that the circuit generating the SLR is mediated through a tectoreticulospinal, rather than a corticospinal, pathway.
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Affiliation(s)
- Chao Gu
- Department of Psychology, University of Western Ontario , London, Ontario , Canada.,The Brain and Mind Institute, University of Western Ontario , London, Ontario , Canada
| | - J Andrew Pruszynski
- Department of Psychology, University of Western Ontario , London, Ontario , Canada.,Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada.,The Brain and Mind Institute, University of Western Ontario , London, Ontario , Canada.,Robarts Research Institute, University of Western Ontario , London, Ontario , Canada
| | - Paul L Gribble
- Department of Psychology, University of Western Ontario , London, Ontario , Canada.,Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada.,The Brain and Mind Institute, University of Western Ontario , London, Ontario , Canada
| | - Brian D Corneil
- Department of Psychology, University of Western Ontario , London, Ontario , Canada.,Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada.,The Brain and Mind Institute, University of Western Ontario , London, Ontario , Canada.,Robarts Research Institute, University of Western Ontario , London, Ontario , Canada
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14
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Goffart L, Cecala AL, Gandhi NJ. The superior colliculus and the steering of saccades toward a moving visual target. J Neurophysiol 2017; 118:2890-2901. [PMID: 28904104 DOI: 10.1152/jn.00506.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Revised: 09/13/2017] [Accepted: 09/13/2017] [Indexed: 11/22/2022] Open
Abstract
Following the suggestion that a command encoding current target location feeds the oculomotor system during interceptive saccades, we tested the involvement of the deep superior colliculus (dSC). Extracellular activity of 52 saccade-related neurons was recorded in three monkeys while they generated saccades to targets that were static or moving along the preferred axis, away from (outward) or toward (inward) a fixated target with a constant speed (20°/s). Vertical and horizontal motions were tested when possible. Movement field (MF) parameters (boundaries, preferred vector, and firing rate) were estimated after spline fitting of the relation between the average firing rate during the motor burst and saccade amplitude. During radial target motions, the inner MF boundary shifted in the motion direction for some, but not all, neurons. Likewise, for some neurons, the lower boundaries were shifted upward during upward motions and the upper boundaries downward during downward motions. No consistent change was observed during horizontal motions. For some neurons, the preferred vectors were also shifted in the motion direction for outward, upward, and "toward the midline" target motions. The shifts of boundary and preferred vector were not correlated. The burst firing rate was consistently reduced during interceptive saccades. Our study demonstrates an involvement of dSC neurons in steering the interceptive saccade. When observed, the shifts of boundary in the direction of target motion correspond to commands related to past target locations. The absence of shift in the opposite direction implies that dSC activity does not issue predictive commands related to future target location.NEW & NOTEWORTHY The deep superior colliculus is involved in steering the saccade toward the current location of a moving target. During interceptive saccades, the active population consists of a continuum of cells ranging from neurons issuing commands related to past locations of the target to neurons issuing commands related to its current location. The motor burst of collicular neurons does not contain commands related to the future location of a moving target.
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Affiliation(s)
- Laurent Goffart
- Institut de Neurosciences de la Timone, UMR 7289 CNRS, Aix-Marseille Université, Marseille, France;
| | - Aaron L Cecala
- Department of Biology, Elizabethtown College, Elizabethtown, Pennsylvania; and
| | - Neeraj J Gandhi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania
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15
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Jagadisan UK, Gandhi NJ. Removal of inhibition uncovers latent movement potential during preparation. eLife 2017; 6:29648. [PMID: 28891467 PMCID: PMC5650474 DOI: 10.7554/elife.29648] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/08/2017] [Indexed: 12/20/2022] Open
Abstract
The motor system prepares for movements well in advance of their execution. In the gaze control system, the dynamics of preparatory neural activity have been well described by stochastic accumulation-to-threshold models. However, it is unclear whether this activity has features indicative of a hidden movement command. We explicitly tested whether preparatory neural activity in premotor neurons of the primate superior colliculus has 'motor potential'. We removed downstream inhibition on the saccadic system using the trigeminal blink reflex, triggering saccades at earlier-than-normal latencies. Accumulating low-frequency activity was predictive of eye movement dynamics tens of milliseconds in advance of the actual saccade, indicating the presence of a latent movement command. We also show that reaching a fixed threshold level is not a necessary condition for movement initiation. The results bring into question extant models of saccade generation and support the possibility of a concurrent representation for movement preparation and generation.
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Affiliation(s)
- Uday K Jagadisan
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, United States.,Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, United States
| | - Neeraj J Gandhi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, United States.,Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, United States.,Department of Otolaryngology, University of Pittsburgh, Pittsburgh, United States.,Department of Neuroscience, University of Pittsburgh, Pittsburgh, United States
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16
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Disruption of Fixation Reveals Latent Sensorimotor Processes in the Superior Colliculus. J Neurosci 2017; 36:6129-40. [PMID: 27251631 DOI: 10.1523/jneurosci.3685-15.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Accepted: 04/12/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Executive control of voluntary movements is a hallmark of the mammalian brain. In the gaze-control network, this function is thought to be mediated by a critical balance between neurons responsible for generating movements and those responsible for fixating or suppressing movements, but the nature of this balance between the relevant elements-saccade-generating and fixation-related neurons-remains unclear. Specifically, it has been debated whether the two functions are necessarily coupled (i.e., push-and-pull) or independently controlled. Here we show that behavioral perturbation of ongoing fixation with the trigeminal blink reflex in monkeys (Macaca mulatta) alters the effective balance between fixation and saccade-generating neurons in the superior colliculus (SC) and can lead to premature gaze shifts reminiscent of compromised inhibitory control. The shift in balance is primarily driven by an increase in the activity of visuomovement neurons in the caudal SC, and the extent to which fixation-related neurons in the rostral SC play a role seems to be linked to the animal's propensity to make microsaccades. The perturbation also reveals a hitherto unknown feature of sensorimotor integration: the presence of a hidden visual response in canonical movement neurons. These findings offer new insights into the latent functional interactions, or lack thereof, between components of the gaze-control network, suggesting that the perturbation technique used here may prove to be a useful tool for probing the neural mechanisms of movement generation in executive function and dysfunction. SIGNIFICANCE STATEMENT Eye movements are an integral part of how we explore the environment. Although we know a great deal about where sensorimotor transformations leading to saccadic eye movements are implemented in the brain, less is known about the functional interactions between neurons that maintain gaze fixation and neurons that program saccades. In this study, we used a novel approach to study these interactions. By transient disruption of fixation, we found that activity of saccade-generating neurons can increase independently of modulation in fixation-related neurons, which may occasionally lead to premature movements mimicking lack of impulse control. Our findings support the notion of a common pathway for sensory and movement processing and suggest that impulsive movements arise when sensory processes become "motorized."
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17
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Abstract
The superior colliculus is one of the most well-studied structures in the brain, and with each new report, its proposed role in behavior seems to increase in complexity. Forty years of evidence show that the colliculus is critical for reorienting an organism toward objects of interest. In monkeys, this involves saccadic eye movements. Recent work in the monkey colliculus and in the homologous optic tectum of the bird extends our understanding of the role of the colliculus in higher mental functions, such as attention and decision making. In this review, we highlight some of these recent results, as well as those capitalizing on circuit-based methodologies using transgenic mice models, to understand the contribution of the colliculus to attention and decision making. The wealth of information we have about the colliculus, together with new tools, provides a unique opportunity to obtain a detailed accounting of the neurons, circuits, and computations that underlie complex behavior.
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Affiliation(s)
- Michele A Basso
- Fuster Laboratory of Cognitive Neuroscience, Department of Psychiatry and Biobehavioral Sciences and Neurobiology, Semel Institute for Neuroscience and Human Behavior, Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, California 90095;
| | - Paul J May
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi 39216
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18
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Megardon G, Ludwig C, Sumner P. Trajectory curvature in saccade sequences: spatiotopic influences vs. residual motor activity. J Neurophysiol 2017; 118:1310-1320. [PMID: 28592684 DOI: 10.1152/jn.00110.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 05/02/2017] [Accepted: 06/01/2017] [Indexed: 11/22/2022] Open
Abstract
When decisions drive saccadic eye movements, traces of the decision process can be inferred from the movement trajectories. For example, saccades can curve away from distractor stimuli, which was thought to reflect cortical inhibition biasing activity in the superior colliculus. Recent neurophysiological work does not support this theory, and two recent models have replaced top-down inhibition with lateral interactions in the superior colliculus or neural fatigue in the brainstem saccadic burst generator. All current models operate in retinotopic coordinates and are based on single saccade paradigms. To extend these models to sequences of saccades, we assessed whether and how saccade curvature depends on previously fixated locations and the direction of previous saccades. With a two-saccade paradigm, we first demonstrated that second saccades curved away from the initial fixation stimulus. Furthermore, by varying the time from fixation offset and the intersaccadic duration, we distinguished the extent of curvature originating from the spatiotopic representation of the previous fixation location or residual motor activity of the previous saccade. Results suggest that both factors drive curvature, and we discuss how these effects could be implemented in current models. In particular, we propose that the collicular retinotopic maps receive an excitatory spatiotopic update from the lateral interparial region.NEW & NOTEWORTHY Saccades curve away from locations of previous fixation. Varying stimulus timing demonstrates the effects of both 1) spatiotopic representation and 2) motor residual activity from previous saccades. The spatiotopic effect can be explained if current models are augmented with an excitatory top-down spatiotopic signal.
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Affiliation(s)
- Geoffrey Megardon
- Cardiff University Brain Research Imagery Centre, School of Psychology, Cardiff University, Cardiff, United Kingdom; .,School of Psychology, Cardiff University, Tower Building, Cardiff, United Kingdom
| | - Casimir Ludwig
- School of Experimental Psychology, University of Bristol, Bristol, United Kingdom; and
| | - Petroc Sumner
- School of Psychology, Cardiff University, Tower Building, Cardiff, United Kingdom
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19
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White BJ, Berg DJ, Kan JY, Marino RA, Itti L, Munoz DP. Superior colliculus neurons encode a visual saliency map during free viewing of natural dynamic video. Nat Commun 2017; 8:14263. [PMID: 28117340 PMCID: PMC5286207 DOI: 10.1038/ncomms14263] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 12/13/2016] [Indexed: 11/24/2022] Open
Abstract
Models of visual attention postulate the existence of a saliency map whose function is to guide attention and gaze to the most conspicuous regions in a visual scene. Although cortical representations of saliency have been reported, there is mounting evidence for a subcortical saliency mechanism, which pre-dates the evolution of neocortex. Here, we conduct a strong test of the saliency hypothesis by comparing the output of a well-established computational saliency model with the activation of neurons in the primate superior colliculus (SC), a midbrain structure associated with attention and gaze, while monkeys watched video of natural scenes. We find that the activity of SC superficial visual-layer neurons (SCs), specifically, is well-predicted by the model. This saliency representation is unlikely to be inherited from fronto-parietal cortices, which do not project to SCs, but may be computed in SCs and relayed to other areas via tectothalamic pathways.
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Affiliation(s)
- Brian J. White
- Centre for Neuroscience Studies, Queen's University, 18 Stuart St, Kingston, Ontario, Canada K7L3N6
| | - David J. Berg
- IBM Research, Almaden, 650 Harry Road, San Jose, California 95120, USA
| | - Janis Y. Kan
- Centre for Neuroscience Studies, Queen's University, 18 Stuart St, Kingston, Ontario, Canada K7L3N6
| | - Robert A. Marino
- Centre for Neuroscience Studies, Queen's University, 18 Stuart St, Kingston, Ontario, Canada K7L3N6
| | - Laurent Itti
- Department of Computer Science, University of Southern California, 0781, 941 Bloom Walk, Los Angeles, California 90089, USA
| | - Douglas P. Munoz
- Centre for Neuroscience Studies, Queen's University, 18 Stuart St, Kingston, Ontario, Canada K7L3N6
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20
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Sadeh M, Sajad A, Wang H, Yan X, Crawford JD. Spatial transformations between superior colliculus visual and motor response fields during head-unrestrained gaze shifts. Eur J Neurosci 2016; 42:2934-51. [PMID: 26448341 DOI: 10.1111/ejn.13093] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2014] [Revised: 09/14/2015] [Accepted: 09/30/2015] [Indexed: 11/27/2022]
Abstract
We previously reported that visuomotor activity in the superior colliculus (SC)--a key midbrain structure for the generation of rapid eye movements--preferentially encodes target position relative to the eye (Te) during low-latency head-unrestrained gaze shifts (DeSouza et al., 2011). Here, we trained two monkeys to perform head-unrestrained gaze shifts after a variable post-stimulus delay (400-700 ms), to test whether temporally separated SC visual and motor responses show different spatial codes. Target positions, final gaze positions and various frames of reference (eye, head, and space) were dissociated through natural (untrained) trial-to-trial variations in behaviour. 3D eye and head orientations were recorded, and 2D response field data were fitted against multiple models by use of a statistical method reported previously (Keith et al., 2009). Of 60 neurons, 17 showed a visual response, 12 showed a motor response, and 31 showed both visual and motor responses. The combined visual response field population (n = 48) showed a significant preference for Te, which was also preferred in each visual subpopulation. In contrast, the motor response field population (n = 43) showed a preference for final (relative to initial) gaze position models, and the Te model was statistically eliminated in the motor-only population. There was also a significant shift of coding from the visual to motor response within visuomotor neurons. These data confirm that SC response fields are gaze-centred, and show a target-to-gaze transformation between visual and motor responses. Thus, visuomotor transformations can occur between, and even within, neurons within a single frame of reference and brain structure.
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Affiliation(s)
- Morteza Sadeh
- York Centre for Vision Research, Room 0009A LAS, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.,York Neuroscience Graduate Diploma Program, Toronto, ON, Canada.,Canadian Action and Perception Network (CAPnet), York University, Toronto, ON, Canada.,Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, ON, Canada
| | - Amirsaman Sajad
- York Centre for Vision Research, Room 0009A LAS, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.,York Neuroscience Graduate Diploma Program, Toronto, ON, Canada.,Canadian Action and Perception Network (CAPnet), York University, Toronto, ON, Canada.,Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, ON, Canada
| | - Hongying Wang
- York Centre for Vision Research, Room 0009A LAS, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.,Canadian Action and Perception Network (CAPnet), York University, Toronto, ON, Canada.,Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, ON, Canada
| | - Xiaogang Yan
- York Centre for Vision Research, Room 0009A LAS, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.,Canadian Action and Perception Network (CAPnet), York University, Toronto, ON, Canada.,Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, ON, Canada
| | - John Douglas Crawford
- York Centre for Vision Research, Room 0009A LAS, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.,York Neuroscience Graduate Diploma Program, Toronto, ON, Canada.,Canadian Action and Perception Network (CAPnet), York University, Toronto, ON, Canada.,Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, ON, Canada
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21
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Marino RA, Levy R, Munoz DP. Linking express saccade occurance to stimulus properties and sensorimotor integration in the superior colliculus. J Neurophysiol 2015; 114:879-92. [PMID: 26063770 DOI: 10.1152/jn.00047.2015] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Accepted: 06/05/2015] [Indexed: 11/22/2022] Open
Abstract
Express saccades represent the fastest possible eye movements to visual targets with reaction times that approach minimum sensory-motor conduction delays. Previous work in monkeys has identified two specific neural signals in the superior colliculus (SC: a midbrain sensorimotor integration structure involved in gaze control) that are required to execute express saccades: 1) previsual activity consisting of a low-frequency increase in action potentials in sensory-motor neurons immediately before the arrival of a visual response; and 2) a transient visual-sensory response consisting of a high-frequency burst of action potentials in visually responsive neurons resulting from the appearance of a visual target stimulus. To better understand how these two neural signals interact to produce express saccades, we manipulated the arrival time and magnitude of visual responses in the SC by altering target luminance and we examined the corresponding influences on SC activity and express saccade generation. We recorded from saccade neurons with visual-, motor-, and previsual-related activity in the SC of monkeys performing the gap saccade task while target luminance was systematically varied between 0.001 and 42.5 cd/m(2) against a black background (∼0.0001 cd/m(2)). Our results demonstrated that 1) express saccade latencies were linked directly to the arrival time in the SC of visual responses produced by abruptly appearing visual stimuli; 2) express saccades were generated toward both dim and bright targets whenever sufficient previsual activity was present; and 3) target luminance altered the likelihood of producing an express saccade. When an express saccade was generated, visuomotor neurons increased their activity immediately before the arrival of the visual response in the SC and saccade initiation. Furthermore, the visual and motor responses of visuomotor neurons merged into a single burst of action potentials, while the visual response of visual-only neurons was unaffected. A linear combination model was used to test which SC signals best predicted the likelihood of producing an express saccade. In addition to visual response magnitude and previsual activity of saccade neurons, the model identified presaccadic activity (activity occurring during the 30-ms epoch immediately before saccade initiation) as a third important signal for predicting express saccades. We conclude that express saccades can be predicted by visual, previsual, and presaccadic signals recorded from visuomotor neurons in the intermediate layers of the SC.
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Affiliation(s)
- Robert A Marino
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada; Department of Surgery, Kingston General Hospital, Kingston, Ontario, Canada
| | - Ron Levy
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada; Department of Medicine, Queen's University, Kingston, Ontario, Canada; and Department of Surgery, Kingston General Hospital, Kingston, Ontario, Canada
| | - Douglas P Munoz
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada; Department of Biomedical and Molecular Science, Queen's University, Kingston, Ontario, Canada; Department of Psychology, Queen's University, Kingston, Ontario, Canada; Department of Medicine, Queen's University, Kingston, Ontario, Canada; and
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22
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Abstract
Searching for a visual object naturally involves sequences of gaze fixations, during which the current foveal image is analyzed and the next object to inspect is selected as a saccade target. Fixation durations during such sequences are short, suggesting that saccades may be concurrently processed. Therefore, the selection of the next saccade target may occur before the current saccade target is acquired. To test this hypothesis, we trained four female rhesus monkeys (Macaca mulatta) to perform a multiple-fixation visual conjunction search task. We simultaneously recorded the activity of sensorimotor neurons in the midbrain superior colliculus (SC) in two monkeys. In this task, monkeys made multiple fixations before foveating the target. Fixation durations were significantly shorter than the latency of the initial responses to the search display, with approximately one-quarter being shorter than the shortest response latencies. The time at which SC sensorimotor activity discriminated the target from distracters occurred significantly earlier for the selection of subsequent fixations than for the selection of the first fixation. Target selection during subsequent fixations occurred even before the visual afferent delay in more than half of the neuronal sample, suggesting that the process of selection can encompass at least two future saccade targets. This predictive selection was present even when differences in saccade latencies were taken into account. Altogether, these findings demonstrate how neural representations on the visual salience map are processed in parallel, thus facilitating visual search.
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23
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24
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Hutchinson M, Isa T, Molloy A, Kimmich O, Williams L, Molloy F, Moore H, Healy DG, Lynch T, Walsh C, Butler J, Reilly RB, Walsh R, O'Riordan S. Cervical dystonia: a disorder of the midbrain network for covert attentional orienting. Front Neurol 2014; 5:54. [PMID: 24803911 PMCID: PMC4009446 DOI: 10.3389/fneur.2014.00054] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Accepted: 04/03/2014] [Indexed: 01/30/2023] Open
Abstract
While the pathogenesis of cervical dystonia remains unknown, recent animal and clinical experimental studies have indicated its probable mechanisms. Abnormal temporal discrimination is a mediational endophenotype of cervical dystonia and informs new concepts of disease pathogenesis. Our hypothesis is that both abnormal temporal discrimination and cervical dystonia are due to a disorder of the midbrain network for covert attentional orienting caused by reduced gamma-aminobutyric acid (GABA) inhibition, resulting, in turn, from as yet undetermined, genetic mutations. Such disinhibition is (a) subclinically manifested by abnormal temporal discrimination due to prolonged duration firing of the visual sensory neurons in the superficial laminae of the superior colliculus and (b) clinically manifested by cervical dystonia due to disinhibited burst activity of the cephalomotor neurons of the intermediate and deep laminae of the superior colliculus. Abnormal temporal discrimination in unaffected first-degree relatives of patients with cervical dystonia represents a subclinical manifestation of defective GABA activity both within the superior colliculus and from the substantia nigra pars reticulata. A number of experiments are required to prove or disprove this hypothesis.
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Affiliation(s)
- Michael Hutchinson
- Department of Neurology, St. Vincent's University Hospital , Dublin , Ireland ; School of Medicine and Medical Science, University College Dublin , Dublin , Ireland
| | - Tadashi Isa
- Department of Developmental Physiology, National Institute for Physiological Sciences , Okazaki , Japan
| | - Anna Molloy
- Department of Neurology, St. Vincent's University Hospital , Dublin , Ireland ; School of Medicine and Medical Science, University College Dublin , Dublin , Ireland
| | - Okka Kimmich
- Department of Neurology, St. Vincent's University Hospital , Dublin , Ireland ; School of Medicine and Medical Science, University College Dublin , Dublin , Ireland
| | - Laura Williams
- Department of Neurology, St. Vincent's University Hospital , Dublin , Ireland ; School of Medicine and Medical Science, University College Dublin , Dublin , Ireland
| | - Fiona Molloy
- Department of Neurophysiology, Beaumont Hospital , Dublin , Ireland
| | | | - Daniel G Healy
- Department of Neurology, Beaumont Hospital , Dublin , Ireland
| | - Tim Lynch
- Dublin Neurological Institute, Mater Misericordiae Hospital , Dublin , Ireland
| | - Cathal Walsh
- Department of Statistics, Trinity College Dublin , Dublin , Ireland
| | - John Butler
- Trinity Centre for Bioengineering, Trinity College Dublin , Dublin , Ireland
| | - Richard B Reilly
- Trinity Centre for Bioengineering, Trinity College Dublin , Dublin , Ireland
| | - Richard Walsh
- Department of Neurology, The Adelaide and Meath Hospital , Dublin , Ireland
| | - Sean O'Riordan
- Department of Neurology, St. Vincent's University Hospital , Dublin , Ireland ; School of Medicine and Medical Science, University College Dublin , Dublin , Ireland
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25
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Kruijne W, Van der Stigchel S, Meeter M. A model of curved saccade trajectories: spike rate adaptation in the brainstem as the cause of deviation away. Brain Cogn 2014; 85:259-70. [PMID: 24486387 DOI: 10.1016/j.bandc.2014.01.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 12/28/2013] [Accepted: 01/07/2014] [Indexed: 10/25/2022]
Abstract
The trajectory of saccades to a target is often affected whenever there is a distractor in the visual field. Distractors can cause a saccade to deviate towards their location or away from it. The oculomotor mechanisms that produce deviation towards distractors have been thoroughly explored in behavioral, neurophysiological and computational studies. The mechanisms underlying deviation away, on the other hand, remain unclear. Behavioral findings suggest a mechanism of spatially focused, top-down inhibition in a saccade map, and deviation away has become a tool to investigate such inhibition. However, this inhibition hypothesis has little neuroanatomical or neurophysiological support, and recent findings go against it. Here, we propose that deviation away results from an unbalanced saccade drive from the brainstem, caused by spike rate adaptation in brainstem long-lead burst neurons. Adaptation to stimulation in the direction of the distractor results in an unbalanced drive away from it. An existing model of the saccade system was extended with this theory. The resulting model simulates a wide range of findings on saccade trajectories, including findings that have classically been interpreted to support inhibition views. Furthermore, the model replicated the effect of saccade latency on deviation away, but predicted this effect would be absent with large (400 ms) distractor-target onset asynchrony. This prediction was confirmed in an experiment, which demonstrates that the theory both explains classical findings on saccade trajectories and predicts new findings.
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Affiliation(s)
- Wouter Kruijne
- Cognitive Psychology, Faculty of Psychology and Education, Vrije Universiteit Amsterdam, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands.
| | - Stefan Van der Stigchel
- Experimental Psychology, Helmholtz Institute, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands
| | - Martijn Meeter
- Cognitive Psychology, Faculty of Psychology and Education, Vrije Universiteit Amsterdam, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands
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26
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White BJ, Marino RA, Boehnke SE, Itti L, Theeuwes J, Munoz DP. Competitive Integration of Visual and Goal-related Signals on Neuronal Accumulation Rate: A Correlate of Oculomotor Capture in the Superior Colliculus. J Cogn Neurosci 2013; 25:1754-68. [DOI: 10.1162/jocn_a_00429] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Abstract
The mechanisms that underlie the integration of visual and goal-related signals for the production of saccades remain poorly understood. Here, we examined how spatial proximity of competing stimuli shapes goal-directed responses in the superior colliculus (SC), a midbrain structure closely associated with the control of visual attention and eye movements. Monkeys were trained to perform an oculomotor-capture task [Theeuwes, J., Kramer, A. F., Hahn, S., Irwin, D. E., & Zelinsky, G. J. Influence of attentional capture on oculomotor control. Journal of Experimental Psychology. Human Perception and Performance, 25, 1595–1608, 1999], in which a target singleton was revealed via an isoluminant color change in all but one item. On a portion of the trials, an additional salient item abruptly appeared near or far from the target. We quantified how spatial proximity between the abrupt-onset and the target shaped the goal-directed response. We found that the appearance of an abrupt-onset near the target induced a transient decrease in goal-directed discharge of SC visuomotor neurons. Although this was indicative of spatial competition, it was immediately followed by a rebound in presaccadic activation, which facilitated the saccadic response (i.e., it induced shorter saccadic RT). A similar suppression also occurred at most nontarget locations even in the absence of the abrupt-onset. This is indicative of a mechanism that enabled monkeys to quickly discount stimuli that shared the common nontarget feature. These results reveal a pattern of excitation/inhibition across the SC visuomotor map that acted to facilitate optimal behavior—the short duration suppression minimized the probability of capture by salient distractors, whereas a subsequent boost in accumulation rate ensured a fast goal-directed response. Such nonlinear dynamics should be incorporated into future biologically plausible models of saccade behavior.
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Paolozza A, Titman R, Brien D, Munoz DP, Reynolds JN. Altered accuracy of saccadic eye movements in children with fetal alcohol spectrum disorder. Alcohol Clin Exp Res 2013; 37:1491-8. [PMID: 23578065 DOI: 10.1111/acer.12119] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Accepted: 01/21/2013] [Indexed: 11/28/2022]
Abstract
BACKGROUND Prenatal exposure to alcohol is a major, preventable cause of neurobehavioral dysfunction in children worldwide. The measurement and quantification of saccadic eye movements is a powerful tool for assessing sensory, motor, and cognitive function. The quality of the motor process of an eye movement is known as saccade metrics. Saccade accuracy is 1 component of metrics, which to function optimally requires several cortical brain structures as well as an intact cerebellum and brain-stem. The cerebellum has frequently been reported to be damaged by prenatal alcohol exposure. This study, therefore, tested the hypothesis that children with fetal alcohol spectrum disorder (FASD) will exhibit deficits in the accuracy of saccades. METHODS A group of children with FASD (n = 27) between the ages of 8 and 16 and typically developing control children (n = 27) matched for age and sex, completed 3 saccadic eye movement tasks of increasing difficulty. Eye movement performance during the tasks was captured using an infrared eye tracker. Saccade metrics (e.g., velocity, amplitude, accuracy) were quantified and compared between the 2 groups for the 3 different tasks. RESULTS Children with FASD were more variable in saccade endpoint accuracy, which was reflected by statistically significant increases in the error of the initial saccade endpoint and the frequency of additional, corrective saccades required to achieve final fixation. This increased variability in accuracy was amplified when the cognitive demand of the tasks increased. Children with FASD also displayed a statistically significant increase in response inhibition errors. CONCLUSIONS These data suggest that children with FASD may have deficits in eye movement control and sensory-motor integration including cerebellar circuits, thereby impairing saccade accuracy.
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Affiliation(s)
- Angelina Paolozza
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
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28
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Jantz JJ, Watanabe M, Everling S, Munoz DP. Threshold mechanism for saccade initiation in frontal eye field and superior colliculus. J Neurophysiol 2013; 109:2767-80. [PMID: 23486198 DOI: 10.1152/jn.00611.2012] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In an influential model of frontal eye field (FEF) and superior colliculus (SC) activity, saccade initiation occurs when the discharge rate of either single neurons or a population of neurons encoding a saccade motor plan reaches a threshold level of activity. Conflicting evidence exists for whether this threshold is fixed or can change under different conditions. We tested the fixed-threshold hypothesis at the single-neuron and population levels to help resolve the inconsistency between previous studies. Two rhesus monkeys performed a randomly interleaved pro- and antisaccade task in which they had to look either toward (pro) or 180° away (anti) from a peripheral visual stimulus. We isolated visuomotor (VM) and motor (M) neurons in the FEF and SC and tested three specific predictions of a fixed-threshold hypothesis. We found little support for fixed thresholds. First, correlations were never totally absent between presaccadic discharge rate and saccadic reaction time when examining a larger (plausible) temporal period. Second, presaccadic discharge rates varied markedly between saccade tasks. Third, visual responses exceeded presaccadic motor discharges for FEF and SC VM neurons. We calculated that only a remarkably strong bias for M neurons in downstream projections could render the fixed-threshold hypothesis plausible at the population level. Also, comparisons of gap vs. overlap conditions indicate that increased inhibitory tone may be associated with stability of thresholds. We propose that fixed thresholds are the exception rather than the rule in FEF and SC, and that stabilization of an otherwise variable threshold depends on task-related, inhibitory modulation.
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Affiliation(s)
- Jay J Jantz
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
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29
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Gutfreund Y. Stimulus-specific adaptation, habituation and change detection in the gaze control system. BIOLOGICAL CYBERNETICS 2012; 106:657-668. [PMID: 22711216 DOI: 10.1007/s00422-012-0497-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Accepted: 05/23/2012] [Indexed: 06/01/2023]
Abstract
This prospect article addresses the neurobiology of detecting and responding to changes or unexpected events. Change detection is an ongoing computational task performed by the brain as part of the broader process of saliency mapping and selection of the next target for attention. In the optic tectum (OT) of the barn owl, the probability of the stimulus has a dramatic influence on the neural response to that stimulus; rare or deviant stimuli induce stronger responses compared to common stimuli. This phenomenon, known as stimulus-specific adaptation, has recently attracted scientific interest because of its possible role in change detection. In the barn owl's OT, it may underlie the ability to orient specifically to unexpected events and is therefore opening new directions for research on the neurobiology of fundamental psychological phenomena such as habituation, attention, and surprise.
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Affiliation(s)
- Yoram Gutfreund
- The Department of Physiology and Biophysics, Technion, Haifa, Israel.
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30
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Marino RA, Levy R, Boehnke S, White BJ, Itti L, Munoz DP. Linking visual response properties in the superior colliculus to saccade behavior. Eur J Neurosci 2012; 35:1738-52. [DOI: 10.1111/j.1460-9568.2012.08079.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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31
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Wang CA, Boehnke SE, White BJ, Munoz DP. Microstimulation of the monkey superior colliculus induces pupil dilation without evoking saccades. J Neurosci 2012; 32:3629-36. [PMID: 22423086 PMCID: PMC6703448 DOI: 10.1523/jneurosci.5512-11.2012] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 12/22/2011] [Accepted: 01/14/2012] [Indexed: 11/21/2022] Open
Abstract
The orienting reflex is initiated by a salient stimulus and facilitates quick, appropriate action. It involves a rapid shift of the eyes, head, and attention and other physiological responses such as changes in heart rate and transient pupil dilation. The SC is a critical structure in the midbrain that selects incoming stimuli based on saliency and relevance to coordinate orienting behaviors, particularly gaze shifts, but its causal role in pupil dilation remains poorly understood in mammals. Here, we examined the role of the primate SC in the control of pupil dynamics. While requiring monkeys to keep their gaze fixed, we delivered weak electrical microstimulation to the SC, so that saccadic eye movements were not evoked. Pupil size increased transiently after microstimulation of the intermediate SC layers (SCi) and the size of evoked pupil dilation was larger on a dim versus bright background. In contrast, microstimulation of the superficial SC layers did not cause pupil dilation. Thus, the SCi is directly involved not only in shifts of gaze and attention, but also in pupil dilation as part of the orienting reflex, and the function of pupil dilation may be related to increasing visual sensitivity. The shared neural mechanisms suggest that pupil dilation may be associated with covert attention.
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Affiliation(s)
- Chin-An Wang
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Susan E. Boehnke
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Brian J. White
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Douglas P. Munoz
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
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32
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Shen K, Paré M. Neural basis of feature-based contextual effects on visual search behavior. Front Behav Neurosci 2012; 5:91. [PMID: 22287945 PMCID: PMC3258668 DOI: 10.3389/fnbeh.2011.00091] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 12/24/2011] [Indexed: 12/04/2022] Open
Abstract
Searching for a visual object is known to be adaptable to context, and it is thought to result from the selection of neural representations distributed on a visual salience map, wherein stimulus-driven and goal-directed signals are combined. Here we investigated the neural basis of this adaptability by recording superior colliculus (SC) neurons while three female rhesus monkeys (Macaca mulatta) searched with saccadic eye movements for a target presented in an array of visual stimuli whose feature composition varied from trial to trial. We found that sensory-motor activity associated with distracters was enhanced or suppressed depending on the search array composition and that it corresponded to the monkey's search strategy, as assessed by the distribution of the occasional errant saccades. This feature-related modulation occurred independently from the saccade goal and facilitated the process of saccade target selection. We also observed feature-related enhancement in the activity associated with distracters that had been the search target during the previous session. Consistent with recurrent processing, both feature-related neuronal modulations occurred more than 60 ms after the onset of the visually evoked responses, and their near coincidence with the time of saccade target selection suggests that they are integral to this process. These results suggest that SC neuronal activity is shaped by the visual context as dictated by both stimulus-driven and goal-directed signals. Given the close proximity of the SC to the motor circuit, our findings suggest a direct link between perception and action and no need for distinct salience and motor maps.
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Affiliation(s)
- Kelly Shen
- Centre for Neuroscience Studies, Queen's University, Kingston ON, Canada
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33
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White BJ, Theeuwes J, Munoz DP. Interaction between visual- and goal-related neuronal signals on the trajectories of saccadic eye movements. J Cogn Neurosci 2011; 24:707-17. [PMID: 22066585 DOI: 10.1162/jocn_a_00162] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
During natural viewing, the trajectories of saccadic eye movements often deviate dramatically from a straight-line path between objects. In human studies, saccades have been shown to deviate toward or away from salient visual distractors depending on visual- and goal-related parameters, but the neurophysiological basis for this is not well understood. Some studies suggest that deviation toward is associated with competition between simultaneously active sites within the intermediate layers of the superior colliculus (SC), a midbrain structure that integrates sensory and goal-related signals for the production of saccades. In contrast, deviation away is hypothesized to reflect a higher-level process, whereby the neural site associated with the distractor isactively suppressed via a form of endogenous, top-down inhibition. We tested this hypothesis by measuring presaccadic distractor-evoked activation of SC visuomotor neurons while monkeys performed a simple task configured specifically to induce a high degree of saccades that deviate away. In the SC, cognitive processes such as top-down expectation are represented as variation in the sustained, low-frequency presaccadic discharge. We reasoned that any inhibition at the distractor-related locus associated with saccade deviation should affect the excitability of the neuron, thereby affecting the discharge rate. We found that, although the task produced robust deviation away, there was no evidence of a relationship between saccade deviation and distractor-evoked activation outside a short perisaccadic window that began no earlier than 22 msec before saccade onset. This indicates that deviation away is not adequately explained by a form of sustained, top-down inhibition at the distractor-related locus in the SC. The results are discussed in relation to the primary sources of inhibition associated with saccadic control.
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34
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Schall JD, Purcell BA, Heitz RP, Logan GD, Palmeri TJ. Neural mechanisms of saccade target selection: gated accumulator model of the visual-motor cascade. Eur J Neurosci 2011; 33:1991-2002. [PMID: 21645095 DOI: 10.1111/j.1460-9568.2011.07715.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We review a new computational model developed to understand how evidence about stimulus salience in visual search is translated into a saccade command. The model uses the activity of visually responsive neurons in the frontal eye field as evidence for stimulus salience that is accumulated in a network of stochastic accumulators to produce accurate and timely saccades. We discovered that only when the input to the accumulation process was gated could the model account for the variability in search performance and predict the dynamics of movement neuron discharge rates. This union of cognitive modeling and neurophysiology indicates how the visual-motor transformation can occur, and provides a concrete mapping between neuron function and specific cognitive processes.
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Affiliation(s)
- Jeffrey D Schall
- Center for Integrative and Cognitive Neuroscience, Vanderbilt Vision Research Center, Department of Psychology, Vanderbilt University, PMB 407817, 2301 Vanderbilt Place, Nashville, TN 37240-7817, USA.
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35
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Shen K, Valero J, Day GS, Paré M. Investigating the role of the superior colliculus in active vision with the visual search paradigm. Eur J Neurosci 2011; 33:2003-16. [PMID: 21645096 DOI: 10.1111/j.1460-9568.2011.07722.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We review here both the evidence that the functional visuomotor organization of the optic tectum is conserved in the primate superior colliculus (SC) and the evidence for the linking proposition that SC discriminating activity instantiates saccade target selection. We also present new data in response to questions that arose from recent SC visual search studies. First, we observed that SC discriminating activity predicts saccade initiation when monkeys perform an unconstrained search for a target defined by either a single visual feature or a conjunction of two features. Quantitative differences between the results in these two search tasks suggest, however, that SC discriminating activity does not only reflect saccade programming. This finding concurs with visual search studies conducted in posterior parietal cortex and the idea that, during natural active vision, visual attention is shifted concomitantly with saccade programming. Second, the analysis of a large neuronal sample recorded during feature search revealed that visual neurons in the superficial layers do possess discriminating activity. In addition, the hypotheses that there are distinct types of SC neurons in the deeper layers and that they are differently involved in saccade target selection were not substantiated. Third, we found that the discriminating quality of single-neuron activity substantially surpasses the ability of the monkeys to discriminate the target from distracters, raising the possibility that saccade target selection is a noisy process. We discuss these new findings in light of the visual search literature and the view that the SC is a visual salience map for orienting eye movements.
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Affiliation(s)
- Kelly Shen
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
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36
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Marino RA, Trappenberg TP, Dorris M, Munoz DP. Spatial interactions in the superior colliculus predict saccade behavior in a neural field model. J Cogn Neurosci 2011; 24:315-36. [PMID: 21942761 DOI: 10.1162/jocn_a_00139] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
During natural vision, eye movements are dynamically controlled by the combinations of goal-related top-down (TD) and stimulus-related bottom-up (BU) neural signals that map onto objects or locations of interest in the visual world. In primates, both BU and TD signals converge in many areas of the brain, including the intermediate layers of the superior colliculus (SCi), a midbrain structure that contains a retinotopically coded map for saccades. How TD and BU signals combine or interact within the SCi map to influence saccades remains poorly understood and actively debated. It has been proposed that winner-take-all competition between these signals occurs dynamically within this map to determine the next location for gaze. Here, we examine how TD and BU signals interact spatially within an artificial two-dimensional dynamic winner-take-all neural field model of the SCi to influence saccadic RT (SRT). We measured point images (spatially organized population activity on the SC map) physiologically to inform the TD and BU model parameters. In this model, TD and BU signals interacted nonlinearly within the SCi map to influence SRT via changes to the (1) spatial size or extent of individual signals, (2) peak magnitude of individual signals, (3) total number of competing signals, and (4) the total spatial separation between signals in the visual field. This model reproduced previous behavioral studies of TD and BU influences on SRT and accounted for multiple inconsistencies between them. This is achieved by demonstrating how, under different experimental conditions, the spatial interactions of TD and BU signals can lead to either increases or decreases in SRT. Our results suggest that dynamic winner-take-all modeling with local excitation and distal inhibition in two dimensions accurately reflects both the physiological activity within the SCi map and the behavioral changes in SRT that result from BU and TD manipulations.
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37
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Basso MA, Sommer MA. Exploring the role of the substantia nigra pars reticulata in eye movements. Neuroscience 2011; 198:205-12. [PMID: 21884760 DOI: 10.1016/j.neuroscience.2011.08.026] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 08/06/2011] [Accepted: 08/12/2011] [Indexed: 10/17/2022]
Abstract
Experiments that demonstrated a role for the substantia nigra in eye movements have played an important role in our understanding of the function of the basal ganglia in behavior more broadly. In this review we explore more recent experiments that extend the role of the substantia nigra pars reticulata from a simple gate for eye movements to include a role in cognitive processes for eye movements. We review recent evidence suggesting that basal ganglia nuclei beyond the substantia nigra may also play a role in eye movements and the cognitive events leading up to the production of eye movements. We close by pointing out some unresolved questions in our understanding of the relationship of basal ganglia nuclei and eye movements.
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Affiliation(s)
- M A Basso
- Department of Neuroscience, Ophthalmology and Visual Sciences University of Wisconsin Madison, Madison, WI 53706, USA.
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38
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Separate visual signals for saccade initiation during target selection in the primate superior colliculus. J Neurosci 2011; 31:1570-8. [PMID: 21289164 DOI: 10.1523/jneurosci.5349-10.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The primary function of the superior colliculus (SC) is to orient the visual system toward behaviorally relevant stimuli defined by features such as color. However, a longstanding view has held that visual activity in the SC arises exclusively from achromatic pathways. Recently, we reported evidence that the primate SC is highly sensitive to signals originating from chromatic pathways, but these signals are delayed relative to luminance signals (White et al., 2009). Here, we describe a functional consequence of this difference in visual arrival time on the processes leading to target selection and saccade initiation. Two rhesus monkeys performed a simple color-singleton selection task in which stimuli carried a chromatic component only (target and distractors were isoluminant with the background, but differed in chromaticity) or a combined chromatic-achromatic component (36% luminance contrast added equally to all stimuli). Although visual responses were delayed in the chromatic-only relative to the combined chromatic-achromatic condition, SC neurons discriminated the target from distractors at approximately the same time provided stimulus chromaticity was held constant. However, saccades were triggered sooner, and with more errors, with the chromatic-achromatic condition, suggesting that luminance signals associated with these stimuli increased the probability of triggering a saccade before the target color was adequately discriminated. These results suggest that separate mechanisms may independently influence the saccadic command in the SC, one linked to the arrival time of pertinent visual signals, and another linked to the output of the visual selection process.
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39
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Chapman BB, Corneil BD. Neuromuscular recruitment related to stimulus presentation and task instruction during the anti-saccade task. Eur J Neurosci 2010; 33:349-60. [DOI: 10.1111/j.1460-9568.2010.07496.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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40
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Netser S, Ohayon S, Gutfreund Y. Multiple Manifestations of Microstimulation in the Optic Tectum: Eye Movements, Pupil Dilations, and Sensory Priming. J Neurophysiol 2010; 104:108-18. [DOI: 10.1152/jn.01142.2009] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It is well established that the optic tectum (or its mammalian homologue, the superior colliculus) is involved in directing gaze toward salient stimuli. However, salient stimuli typically induce orienting responses beyond gaze shifts. The role of the optic tectum in generating responses such as pupil dilation, galvanic responses, or covert shifts is not clear. In the present work, we studied the effects of microstimulation in the optic tectum of the barn owl ( Tyto alba) on pupil diameter and on eye shifts. Experiments were conducted in lightly anesthetized head-restrained barn owls. We report that low-level microstimulation in the deep layers of the optic tectum readily induced pupil dilation responses (PDRs), as well as small eye movements. Electrically evoked PDRs, similar to acoustically evoked PDRs, were long-lasting and habituated to repeated stimuli. We further show that microstimulation in the external nucleus of the inferior colliculus also induced PDRs. Finally, in experiments in which tectal microstimulations were coupled with acoustic stimuli, we show a tendency of the microstimulation to enhance pupil responses and eye shifts to previously habituated acoustic stimuli. The enhancement was dependent on the site of stimulation in the tectal spatial map; responses to sounds with spatial cues that matched the site of stimulation were more enhanced compared with sounds with spatial cues that did not match. These results suggest that the optic tectum is directly involved in autonomic orienting reflexes as well as in gaze shifts, highlighting the central role of the optic tectum in mediating the body responses to salient stimuli.
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Affiliation(s)
- Shai Netser
- The Department of Physiology and Biophysics, The Rappaport Faculty of Medicine and Research Institute, The Technion–Israel Institute of Technology, Haifa, Israel; and
| | - Shay Ohayon
- Computation and Neural Systems, California Institute of Technology, Pasadena, California
| | - Yoram Gutfreund
- The Department of Physiology and Biophysics, The Rappaport Faculty of Medicine and Research Institute, The Technion–Israel Institute of Technology, Haifa, Israel; and
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41
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Motor output evoked by subsaccadic stimulation of primate frontal eye fields. Proc Natl Acad Sci U S A 2010; 107:6070-5. [PMID: 20231461 DOI: 10.1073/pnas.0911902107] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In addition to its role in shifting the line of sight, the oculomotor system is also involved in the covert orienting of visuospatial attention. Causal evidence supporting this premotor theory of attention, or oculomotor readiness hypothesis, comes from the effect of subsaccadic threshold stimulation of the oculomotor system on behavior and neural activity in the absence of evoked saccades, which parallels the effects of covert attention. Here, by recording neck-muscle activity from monkeys and systematically titrating the level of stimulation current delivered to the frontal eye fields (FEF), we show that such subsaccadic stimulation is not divorced from immediate motor output but instead evokes neck-muscle responses at latencies that approach the minimal conduction time to the motor periphery. On average, neck-muscle thresholds were approximately 25% lower than saccade thresholds, and this difference is larger for FEF sites associated with progressively larger saccades. Importantly, we commonly observed lower neck-muscle thresholds even at sites evoking saccades <or=5 degrees in magnitude, although such small saccades are not associated with head motion. Neck-muscle thresholds compare well with the current levels used in previous studies to influence behavior or neural activity through activation of FEF neurons feeding back to extrastriate cortex. Our results complement this previous work by suggesting that the neurobiologic substrate that covertly orients visuospatial attention shares this command with head premotor circuits in the brainstem, culminating with recruitment in the motor periphery.
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42
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Marino RA, Munoz DP. The effects of bottom-up target luminance and top-down spatial target predictability on saccadic reaction times. Exp Brain Res 2009; 197:321-35. [DOI: 10.1007/s00221-009-1919-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Accepted: 06/17/2009] [Indexed: 11/28/2022]
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43
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Iwamoto Y, Kaneko H, Yoshida K, Shimazu H. Role of glycinergic inhibition in shaping activity of saccadic burst neurons. J Neurophysiol 2009; 101:3063-74. [PMID: 19321642 DOI: 10.1152/jn.90565.2008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The immediate premotor signals for saccades are created at the level of medium-lead burst neurons (MLBNs). During fixations, MLBNs receive tonic inhibition from omnipause neurons (OPNs), which use glycine as a neurotransmitter. To elucidate the role of this inhibition, we studied discharge patterns of horizontal MLBNs following iontophoretic application of strychnine, a glycine-receptor antagonist, in alert cats. Three-barrel micropipettes were used for extracellular recording and iontophoresis. After application of strychnine, MLBNs exhibited spontaneous discharge and visual responses during intersaccadic intervals. Spikes were evoked by single-pulse stimulation of the contralateral superior colliculus (SC). These results show that MLBNs receive substantial excitatory input during intersaccadic intervals and that inhibitory action of OPNs is indeed necessary to prevent MLBNs from firing. Strychnine also affected saccade-related activity of MLBNs. The burst of activity, as in normal conditions, declined rapidly before the end of saccades but was followed by low rate spike activity, which continued beyond the end of saccades. This suggests that in normal conditions, the termination of saccades is determined by resumed inhibitory action of OPNs and not by termination of excitatory input to MLBNs. In addition, the firing rate and the number of spikes during saccades increased after strychnine application, suggesting that MLBNs receive glycinergic inhibition of non-OPN origin as well. We conclude that glycinergic inhibition plays essential roles in the maintenance of stable fixation, the termination of saccades, and the regulation of saccade size and velocity.
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Affiliation(s)
- Yoshiki Iwamoto
- Department of Neurophysiology, Doctoral Program in Kansei Behavioral and Brain Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8574, Japan.
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44
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Boehnke SE, Munoz DP. On the importance of the transient visual response in the superior colliculus. Curr Opin Neurobiol 2008; 18:544-51. [PMID: 19059772 DOI: 10.1016/j.conb.2008.11.004] [Citation(s) in RCA: 130] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 11/05/2008] [Accepted: 11/10/2008] [Indexed: 11/26/2022]
Abstract
A salient event in the environment can initiate a complex orienting response that includes a shift in gaze. The midbrain superior colliculus (SC) contains the appropriate circuitry to generate and distribute a signal of the priority of this event, and co-ordinate the orienting response. The magnitude and timing of the short-latency transient visual response in the SC, when combined with cortical inputs signaling stimulus relevance and expectation, influences the type and latency of the orienting response. This signal in the SC is distributed to higher cortical areas to influence visual processing, to the reinforcement learning system to influence future actions, and to premotor circuits, including neck and shoulder muscles, to influence immediate action.
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Affiliation(s)
- Susan E Boehnke
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
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Marino RA, Rodgers CK, Levy R, Munoz DP. Spatial Relationships of Visuomotor Transformations in the Superior Colliculus Map. J Neurophysiol 2008; 100:2564-76. [DOI: 10.1152/jn.90688.2008] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The oculomotor system is well understood compared with other motor systems; however, we do not yet know the spatial details of sensory to motor transformations. This study addresses this issue by quantifying the spatial relationships between visual and motor responses in the superior colliculus (SC), a midbrain structure involved in the transformation of visual information into saccadic motor command signals. We collected extracellular single-unit recordings from 150 visual-motor (VM) and 28 motor (M) neurons in two monkeys trained to perform a nonpredictive visually guided saccade task to 110 possible target locations. Motor related discharge was greater than visual related discharge in 94% (141/150) of the VM neurons. Across the population of VM neurons, the mean locations of the peak visual and motor responses were spatially aligned. The visual response fields (RFs) were significantly smaller than and usually contained within the motor RFs. Converting RFs into the SC coordinate system significantly reduced any misalignment between peak visual and motor locations. RF size increased with increasing eccentricity in visual space but remained invariant on the SC map beyond 1 mm of the rostral pole. RF shape was significantly more symmetric in SC map coordinates compared with visual space coordinates. These results demonstrate that VM neurons specify the same location of a target stimulus in the visual field as the intended location of an upcoming saccade with minimal misalignment to downstream structures. The computational consequences of spatially transforming visual field coordinates to the SC map resulted in increased alignment and spatial symmetry during visual-sensory to saccadic-motor transformations.
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Liu P, Basso MA. Substantia nigra stimulation influences monkey superior colliculus neuronal activity bilaterally. J Neurophysiol 2008; 100:1098-112. [PMID: 18579662 DOI: 10.1152/jn.01043.2007] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The inhibitory drive arising from the basal ganglia is thought to prevent the occurrence of orienting movements of the eyes, head, and body in monkeys and other mammals. The direct projection from the substantia nigra pars reticulata (SNr) to the superior colliculus (SC) mediates the inhibition. Since the original experiments in the SNr of monkeys the buildup or prelude neuron has been a focus of SC research. However, whether the SNr influences buildup neurons in SC is unknown. Furthermore, a contralateral SNr-SC pathway is evident in many species but remains unexplored in the alert monkey. Here we introduced electrical stimulation of one or both SNr nuclei while recording from SC buildup neurons. Stimulation of the SNr reduced the discharge rate of SC buildup neurons bilaterally. This result is consistent with activation of an inhibitory drive from SNr to SC. The time course of the influence of ipsilateral SNr on the activity of most SC neurons was longer (approximately 73 ms) than the influence of the contralateral SNr (approximately 34 ms). We also found that the variability of saccade onset time and saccade direction was altered with electrical stimulation of the SNr. Taken together our results show that electrical stimulation activates the inhibitory output of the SNr that in turn, reduces the activity of SC buildup neurons in both hemispheres. However, rather than acting as a gate for saccade initiation, the results suggest that the influence of SNr inhibition on visually guided saccades is more subtle, shaping the balance of excitation and inhibition across the SC.
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Affiliation(s)
- Ping Liu
- Department of Physiology, University of Wisconsin-Madison, 1300 University Ave., Room 127 SM1, Madison, WI 53706, USA
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Rezvani S, Corneil BD. Recruitment of a head-turning synergy by low-frequency activity in the primate superior colliculus. J Neurophysiol 2008; 100:397-411. [PMID: 18497351 DOI: 10.1152/jn.90223.2008] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Low-frequency activity within the oculomotor system helps bridge sensation and action. Given ocular stability, low-frequency activity sustained by some neurons within the intermediate and deep superior colliculus (dSC) is assumed to be separated from motor output. However, the dSC is an orienting structure and the influence of low-frequency dSC activity at other effectors remains untested. We studied this by simultaneously recording activity from saccade-related dSC neurons and electromyographic (EMG) activity from neck muscles that turn the head. Monkeys performed a gap-saccade paradigm with varying levels of reward expectancy. Despite head restraint and even for relatively small target eccentricities (<or=10 degrees ), increasing reward expectancy for a given target increased the level of low-frequency activity on dSC neurons encoding saccades to the rewarded target and increased the recruitment of a neck muscle synergy that would turn the head toward the target. The magnitude of neck muscle recruitment correlated positively on a trial-by-trial basis with the level of low-frequency dSC activity, and such correlations were optimized when neck muscle activity was shifted about 20 ms later to account for delays in the tecto-reticulo-spinal pathway. Further, dSC activity discriminated about the side of target presentation approximately 11 ms earlier than neck EMG activity. Considered alongside neck EMG responses evoked causally by SC stimulation, our results are consistent with low-frequency dSC activity recruiting a head-turning synergy. Our results support a brain stem circuit wherein the magnitude of neck muscle recruitment reflects the difference in comparative low-frequency activation across both dSCs, perhaps because of mutually inhibitory interactions within downstream head premotor circuits.
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Affiliation(s)
- Sam Rezvani
- Canadian Institutes of Health Research Group in Action and Perception, London, Ontario, Canada
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48
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Abstract
How the brain selects goals for movements remains unknown. The system designed to move the eyes rapidly, the saccadic system, may play a role. Here we ask how sensory signals within a saccade area are influenced by selecting and preparing a saccade. Trained monkeys made or withheld saccades, based on a color cue, to targets varying in luminance contrast. We measured the initial visual activity of superior colliculus (SC) neurons in response to the appearance of these targets. We determined neuronal contrast responses in three task conditions: when two luminance gratings appeared one in the response field (RF) and one in the mirror-opposite location and a cue to select the stimulus in the RF occurred; when the gratings appeared and a cue to select the stimulus out of the RF occurred; and third, when the gratings appeared but monkeys remained fixating on the central spot. SC neurons had increases in visual responses when contrast increased. Receiver operating characteristic analysis revealed an increased ability of neurons to detect the grating on trials with higher contrast targets and also on trials with a cue to make a saccade compared with trials with a cue to remain fixating. Using two measures of neuronal sensitivity, those SC neurons considered part of the motor circuitry increased their sensitivity to contrast with a cue to make a saccade. The results indicate that movement commands influence sensory responses in SC in much the same way that commands to shift attention influence sensory responses in extrastriate cortex.
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49
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Saccade target selection in the superior colliculus: a signal detection theory approach. J Neurosci 2008; 28:2991-3007. [PMID: 18354003 DOI: 10.1523/jneurosci.5424-07.2008] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
How the brain selects one action from among multiple options is unknown. A main tenet of signal detection theory (SDT) is that sensory stimuli are represented as noisy information channels. Therefore, the accuracy of selection might be predicted by how well neuronal activity representing alternatives can be distinguished. Here, we apply an SDT framework to a motor system by recording from superior colliculus (SC) neurons during performance of a color, oddball selection task. We recorded from sets of four neurons simultaneously, each of the four representing one of the four possible targets. Because the electrode placement constrained the position of the stimuli in the visual field, the stimulus arrangement varied across experiments. This variability in stimulus arrangement led to variability in choices allowing us to explore the relationship between SC neuronal activity and performance accuracy. SC target neurons had higher levels of discharge than SC distractor neurons in subsets of trials when selection performance was very accurate. In subsets of trials when performance was poor, the discharge level decreased in target neurons and increased in distractor neurons. Accurate performance was associated with larger separations between neuronal activity from targets and distractors as quantified by the receiver operating characteristic (ROC) area and d' (an index of discriminability). Poorer performance was associated with less separation of target and distractor neuronal activity. ROC area and d' scaled approximately linearly with performance accuracy. Furthermore, ROC area and d' increased as saccade onset approached. Together, the results indicate that SC buildup neuronal activity signals the saccadic eye movement decision.
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Bottaro A, Yasutake Y, Nomura T, Casadio M, Morasso P. Bounded stability of the quiet standing posture: an intermittent control model. Hum Mov Sci 2008; 27:473-95. [PMID: 18342382 DOI: 10.1016/j.humov.2007.11.005] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2007] [Revised: 11/10/2007] [Accepted: 11/26/2007] [Indexed: 10/22/2022]
Abstract
The paper presents a control model of body sway in quiet standing, which aims at achieving bounded stability by means of an intermittent control mechanism. Control bursts are generated when the current state vector exits an area of uncertainty around the reference point in the phase plane. This area is determined by the limited resolution of proprioceptive signals and the burst generation mechanism is predictive in the sense that it incorporates a rough, but working knowledge (internal model) of the biomechanics of the human inverted pendulum. We show that such a model, in spite of its simplicity and of the fact that it relies on very noisy measurements, is robust and can explain in a detailed way the measured sway patterns.
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Affiliation(s)
- Alessandra Bottaro
- Neurolab, DIST (Department of Informatics, Systems, Telecommunications), University of Genova, Via Opera Pia 13, 16145 Genova, Italy
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