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Alexander AS, Robinson JC, Stern CE, Hasselmo ME. Gated transformations from egocentric to allocentric reference frames involving retrosplenial cortex, entorhinal cortex, and hippocampus. Hippocampus 2023; 33:465-487. [PMID: 36861201 PMCID: PMC10403145 DOI: 10.1002/hipo.23513] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 01/22/2023] [Accepted: 01/25/2023] [Indexed: 03/03/2023]
Abstract
This paper reviews the recent experimental finding that neurons in behaving rodents show egocentric coding of the environment in a number of structures associated with the hippocampus. Many animals generating behavior on the basis of sensory input must deal with the transformation of coordinates from the egocentric position of sensory input relative to the animal, into an allocentric framework concerning the position of multiple goals and objects relative to each other in the environment. Neurons in retrosplenial cortex show egocentric coding of the position of boundaries in relation to an animal. These neuronal responses are discussed in relation to existing models of the transformation from egocentric to allocentric coordinates using gain fields and a new model proposing transformations of phase coding that differ from current models. The same type of transformations could allow hierarchical representations of complex scenes. The responses in rodents are also discussed in comparison to work on coordinate transformations in humans and non-human primates.
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Affiliation(s)
- Andrew S Alexander
- Center for Systems Neuroscience, Boston University, Boston, Massachusetts, USA
| | - Jennifer C Robinson
- Center for Systems Neuroscience, Boston University, Boston, Massachusetts, USA
| | - Chantal E Stern
- Center for Systems Neuroscience, Boston University, Boston, Massachusetts, USA
| | - Michael E Hasselmo
- Center for Systems Neuroscience, Boston University, Boston, Massachusetts, USA
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2
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Vasopressin as a Possible Link between Sleep-Disturbances and Memory Problems. Int J Mol Sci 2022; 23:ijms232415467. [PMID: 36555107 PMCID: PMC9778878 DOI: 10.3390/ijms232415467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 11/18/2022] [Accepted: 12/01/2022] [Indexed: 12/12/2022] Open
Abstract
Normal biological rhythms, including sleep, are very important for a healthy life and their disturbance may induce-among other issues-memory impairment, which is a key problem of many psychiatric pathologies. The major brain center of circadian regulation is the suprachiasmatic nucleus, and vasopressin (AVP), which is one of its main neurotransmitters, also plays a key role in memory formation. In this review paper, we aimed to summarize our knowledge on the vasopressinergic connection between sleep and memory with the help of the AVP-deficient Brattleboro rat strain. These animals have EEG disturbances with reduced sleep and impaired memory-boosting theta oscillation and show memory impairment in parallel. Based upon human and animal data measuring AVP levels, haplotypes, and the administration of AVP or its agonist or antagonist via different routes (subcutaneous, intraperitoneal, intracerebroventricular, or intranasal), V1a receptors (especially of hippocampal origin) were implicated in the sleep-memory interaction. All in all, the presented data confirm the possible connective role of AVP between biological rhythms and memory formation, thus, supporting the importance of AVP in several psychopathological conditions.
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3
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Tukker JJ, Beed P, Brecht M, Kempter R, Moser EI, Schmitz D. Microcircuits for spatial coding in the medial entorhinal cortex. Physiol Rev 2021; 102:653-688. [PMID: 34254836 PMCID: PMC8759973 DOI: 10.1152/physrev.00042.2020] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The hippocampal formation is critically involved in learning and memory and contains a large proportion of neurons encoding aspects of the organism’s spatial surroundings. In the medial entorhinal cortex (MEC), this includes grid cells with their distinctive hexagonal firing fields as well as a host of other functionally defined cell types including head direction cells, speed cells, border cells, and object-vector cells. Such spatial coding emerges from the processing of external inputs by local microcircuits. However, it remains unclear exactly how local microcircuits and their dynamics within the MEC contribute to spatial discharge patterns. In this review we focus on recent investigations of intrinsic MEC connectivity, which have started to describe and quantify both excitatory and inhibitory wiring in the superficial layers of the MEC. Although the picture is far from complete, it appears that these layers contain robust recurrent connectivity that could sustain the attractor dynamics posited to underlie grid pattern formation. These findings pave the way to a deeper understanding of the mechanisms underlying spatial navigation and memory.
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Affiliation(s)
- John J Tukker
- Network Dysfunction, German Center for Neurodegenerative Diseases, Berlin, Germany
| | - Prateep Beed
- NeuroScientific Research Center, Charite Berlin, Germany
| | - Michael Brecht
- Systems Neuroscience, Humboldt University of Berlin, Berlin, Germany
| | - Richard Kempter
- Department of Biology, Institute for Theoretical Biology, Humbolt-Universität zu Berlin, Berlin, Germany
| | - Edvard I Moser
- Kavli Institute for Systems Neuroscience and Centre for the Biology of Memory, Norwegian University of Science and Technology
| | - Dietmar Schmitz
- Neuroscience Research Center, Charité Universitätsmedizin Berlin, Berlin, Germany
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4
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Abstract
The entorhinal cortex (EC) is a critical element of the hippocampal formation located within the medial temporal lobe (MTL) in primates. The EC has historically received attention for being the primary mediator of cortical information going into and coming from the hippocampus proper. In this review, we highlight the significance of the EC as a major player in memory processing, along with other associated structures in the primate MTL. The complex, convergent topographies of cortical and subcortical input to the EC, combined with short-range intrinsic connectivity and the selective targeting of EC efferents to the hippocampus, provide evidence for subregional specialization and integration of information beyond what would be expected if this structure were a simple conduit of information for the hippocampus. Lesion studies of the EC provide evidence implicating this region as critical for memory and the flexible use of complex relational associations between experienced events. The physiology of this structure's constituent principal cells mirrors the complexity of its anatomy. EC neurons respond preferentially to aspects of memory-dependent paradigms including object, place, and time. EC neurons also show striking spatial representations as primates explore visual space, similar to those identified in rodents navigating physical space. In this review, we highlight the great strides that have been made toward furthering our understanding of the primate EC, and we identify paths forward for future experiments to provide additional insight into the role of this structure in learning and memory.
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Affiliation(s)
- Aaron D Garcia
- Graduate Program in Neuroscience, University of Washington, Seattle, Washington 98195, USA.,Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, Washington 98195, USA;
| | - Elizabeth A Buffalo
- Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle, Washington 98195, USA; .,Washington National Primate Research Center, University of Washington, Seattle, Washington 98195, USA
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5
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Doucet G, Gulli RA, Corrigan BW, Duong LR, Martinez-Trujillo JC. Modulation of local field potentials and neuronal activity in primate hippocampus during saccades. Hippocampus 2019; 30:192-209. [PMID: 31339193 DOI: 10.1002/hipo.23140] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Revised: 06/26/2019] [Accepted: 06/28/2019] [Indexed: 01/15/2023]
Abstract
Primates use saccades to gather information about objects and their relative spatial arrangement, a process essential for visual perception and memory. It has been proposed that signals linked to saccades reset the phase of local field potential (LFP) oscillations in the hippocampus, providing a temporal window for visual signals to activate neurons in this region and influence memory formation. We investigated this issue by measuring hippocampal LFPs and spikes in two macaques performing different tasks with unconstrained eye movements. We found that LFP phase clustering (PC) in the alpha/beta (8-16 Hz) frequencies followed foveation onsets, while PC in frequencies lower than 8 Hz followed spontaneous saccades, even on a homogeneous background. Saccades to a solid grey background were not followed by increases in local neuronal firing, whereas saccades toward appearing visual stimuli were. Finally, saccade parameters correlated with LFPs phase and amplitude: saccade direction correlated with delta (≤4 Hz) phase, and saccade amplitude with theta (4-8 Hz) power. Our results suggest that signals linked to saccades reach the hippocampus, producing synchronization of delta/theta LFPs without a general activation of local neurons. Moreover, some visual inputs co-occurring with saccades produce LFP synchronization in the alpha/beta bands and elevated neuronal firing. Our findings support the hypothesis that saccade-related signals enact sensory input-dependent plasticity and therefore memory formation in the primate hippocampus.
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Affiliation(s)
- Guillaume Doucet
- The Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.,Department of Physiology, McGill University, Montreal, Quebec, Canada.,Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Roberto A Gulli
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada.,Department of Neuroscience, Columbia University, New York, New York
| | - Benjamin W Corrigan
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada
| | - Lyndon R Duong
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Center for Neural Science, New York University, New York, New York
| | - Julio C Martinez-Trujillo
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Robarts Research Institute, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Department of Psychiatry, Schulich School of Medicine and Dentistry, Western University, London, Ontario, Canada.,Brain and Mind Institute, Western University, London, Ontario, Canada
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6
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M Aghajan Z, Schuette P, Fields TA, Tran ME, Siddiqui SM, Hasulak NR, Tcheng TK, Eliashiv D, Mankin EA, Stern J, Fried I, Suthana N. Theta Oscillations in the Human Medial Temporal Lobe during Real-World Ambulatory Movement. Curr Biol 2017; 27:3743-3751.e3. [PMID: 29199073 DOI: 10.1016/j.cub.2017.10.062] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 09/21/2017] [Accepted: 10/25/2017] [Indexed: 01/24/2023]
Abstract
The theta rhythm-a slow (6-12 Hz) oscillatory component of the local field potential-plays a critical role in spatial navigation and memory by coordinating the activity of neuronal ensembles within the medial temporal lobe (MTL). Although theta has been extensively studied in freely moving rodents, its presence in humans has been elusive and primarily investigated in stationary subjects. Here we used a unique clinical opportunity to examine theta within the human MTL during untethered, real-world ambulatory movement. We recorded intracranial electroencephalographic activity from participants chronically implanted with the wireless NeuroPace responsive neurostimulator (RNS) and tracked their motion with sub-millimeter precision. Our data revealed that movement-related theta oscillations indeed exist in humans, such that theta power is significantly higher during movement than immobility. Unlike in rodents, however, theta occurs in short bouts, with average durations of ∼400 ms, which are more prevalent during fast versus slow movements. In a rare opportunity to study a congenitally blind participant, we found that both the prevalence and duration of theta bouts were increased relative to the sighted participants. These results provide critical support for conserved neurobiological characteristics of theta oscillations during ambulatory spatial navigation, while highlighting some fundamental differences across species in these oscillations between humans and rodents.
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Affiliation(s)
- Zahra M Aghajan
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Peter Schuette
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Tony A Fields
- Department of Neurology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Michelle E Tran
- Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Sameed M Siddiqui
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | | | | | - Dawn Eliashiv
- Department of Neurology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Emily A Mankin
- Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - John Stern
- Department of Neurology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Itzhak Fried
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, CA 90095, USA; Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Functional Neurosurgery Unit, Tel Aviv Medical Center, Tel Aviv 64361, Israel; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
| | - Nanthia Suthana
- Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, CA 90095, USA; Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Department of Psychology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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7
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Abstract
Current interpretations of hippocampal memory function are blind to the fact that viewing behaviors are pervasive and complicate the relationships among perception, behavior, memory, and brain activity. For example, hippocampal activity and associative memory demands increase with stimulus complexity. Stimulus complexity also strongly modulates viewing. Associative processing and viewing thus are often confounded, rendering interpretation of hippocampal activity ambiguous. Similar considerations challenge many accounts of hippocampal function. To explain relationships between memory and viewing, we propose that the hippocampus supports the online memory demands necessary to guide visual exploration. The hippocampus thus orchestrates memory-guided exploration that unfolds over time to build coherent memories. This new perspective on hippocampal function harmonizes with the fact that memory formation and exploratory viewing are tightly intertwined.
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8
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Meister MLR, Buffalo EA. Getting directions from the hippocampus: The neural connection between looking and memory. Neurobiol Learn Mem 2016; 134 Pt A:135-144. [PMID: 26743043 PMCID: PMC4927424 DOI: 10.1016/j.nlm.2015.12.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 12/12/2015] [Accepted: 12/16/2015] [Indexed: 01/29/2023]
Abstract
Investigations into the neural basis of memory in human and non-human primates have focused on the hippocampus and associated medial temporal lobe (MTL) structures. However, how memory signals from the hippocampus affect motor actions is unknown. We propose that approaching this question through eye movement, especially by assessing the changes in looking behavior that occur with experience, is a promising method for exposing neural computations within the hippocampus. Here, we review how looking behavior is guided by memory in several ways, some of which have been shown to depend on the hippocampus, and how hippocampal neural signals are modulated by eye movements. Taken together, these findings highlight the need for future research on how MTL structures interact with the oculomotor system. Probing how the hippocampus reflects and impacts motor output during looking behavior renders a practical path to advance our understanding of the hippocampal memory system.
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Affiliation(s)
- Miriam L R Meister
- Department of Physiology and Biophysics, University of Washington, USA; Washington National Primate Research Center, USA; University of Washington School of Medicine, USA
| | - Elizabeth A Buffalo
- Department of Physiology and Biophysics, University of Washington, USA; Washington National Primate Research Center, USA; University of Washington School of Medicine, USA
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9
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Eichenbaum H, Amaral DG, Buffalo EA, Buzsáki G, Cohen N, Davachi L, Frank L, Heckers S, Morris RGM, Moser EI, Nadel L, O'Keefe J, Preston A, Ranganath C, Silva A, Witter M. Hippocampus at 25. Hippocampus 2016; 26:1238-49. [PMID: 27399159 PMCID: PMC5367855 DOI: 10.1002/hipo.22616] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 07/08/2016] [Indexed: 11/08/2022]
Abstract
The journal Hippocampus has passed the milestone of 25 years of publications on the topic of a highly studied brain structure, and its closely associated brain areas. In a recent celebration of this event, a Boston memory group invited 16 speakers to address the question of progress in understanding the hippocampus that has been achieved. Here we present a summary of these talks organized as progress on four main themes: (1) Understanding the hippocampus in terms of its interactions with multiple cortical areas within the medial temporal lobe memory system, (2) understanding the relationship between memory and spatial information processing functions of the hippocampal region, (3) understanding the role of temporal organization in spatial and memory processing by the hippocampus, and (4) understanding how the hippocampus integrates related events into networks of memories. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Howard Eichenbaum
- Center for Memory and Brain and Department of Psychological and Brain Sciences, Boston University, Boston, MA.
| | - David G Amaral
- Department of Psychiatry and Behavioral Sciences and UC Davis Mind Institute, Davis, CA
| | - Elizabeth A Buffalo
- Department of Physiology and Biophysics, University of Washington, Seattle, WA
| | - György Buzsáki
- Deparment of Neuroscience and Physiology and NYU Neuroscience Institute, New York University Medical School, New York, NY
| | - Neal Cohen
- Psychology Department and Beckman Institute, University of Illinois at Urbana Champaign, Champaign, IL
| | - Lila Davachi
- Department of Psychology, New York Institute, New York, NY
| | - Loren Frank
- Department of Physiology and Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA
| | - Stephan Heckers
- Department of Psychiatry and Behavioral Sciences, Vanderbilt University School of Medicine, Nashville, TN
| | - Richard G M Morris
- Centre for Cognitive and Neural Systems,The University of Edinburgh, Edinburgh, UK
| | - Edvard I Moser
- Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, Trondheim, Norway
| | - Lynn Nadel
- Department of Psychology, University of Arizona, Tucson, AZ
| | - John O'Keefe
- Sainsbury Wellcome Centre for Neural Circuits and Behaviour and Department of Cell and Developmental Biology, University College London, UK
| | - Alison Preston
- Center for Learning and Memory, Department of Psychology and Neuroscience, University of Texas at Austin, Austin, TX
| | - Charan Ranganath
- Department of Psychiatry and Behavioral Sciences and UC Davis Mind Institute, Davis, CA
| | - Alcino Silva
- Department of Psychology and Brain Research Institute, University of California, Los Angeles, Los Angeles, CA
| | - Menno Witter
- Kavli Institute for Systems Neuroscience and Centre for Neural Computation, Norwegian University of Science and Technology, Trondheim, Norway
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10
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Womelsdorf T, Everling S. Long-Range Attention Networks: Circuit Motifs Underlying Endogenously Controlled Stimulus Selection. Trends Neurosci 2016; 38:682-700. [PMID: 26549883 DOI: 10.1016/j.tins.2015.08.009] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 08/24/2015] [Accepted: 08/27/2015] [Indexed: 11/19/2022]
Abstract
Attention networks comprise brain areas whose coordinated activity implements stimulus selection. This selection is reflected in spatially referenced priority maps across frontal-parietal-collicular areas and is controlled through interactions with circuits representing behavioral goals, including prefrontal, cingulate, and striatal circuits, among others. We review how these goal-providing structures control stimulus selection through long-range dynamic projection motifs. These motifs (i) combine feature-tuned subnetworks to a distributed priority map, (ii) establish endogenously controlled, long-range coherent activity at 4-10 Hz theta and 12-30 Hz beta-band frequencies, and (iii) are composed of unique cell types implementing long-range networks through disynaptic disinhibition, dendritic gating, and feedforward inhibitory gain control. This evidence reveals common circuit motifs used to coordinate attentionally selected information across multi-node brain networks during goal-directed behavior.
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Affiliation(s)
- Thilo Womelsdorf
- Department of Biology, Centre for Vision Research, York University, 4700 Keele Street, Toronto, Ontario M6J 1P3, Canada.
| | - Stefan Everling
- Department of Physiology and Pharmacology, Centre for Functional and Metabolic Mapping, University of Western Ontario, 1151 Richmond Street North, Ontario N6A 5B7, Canada
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11
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Rightward-biased hemodynamic response of the parahippocampal system during virtual navigation. Sci Rep 2015; 5:9063. [PMID: 25761577 PMCID: PMC4356951 DOI: 10.1038/srep09063] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 01/28/2015] [Indexed: 11/20/2022] Open
Abstract
Phase reset of parahippocampal electrophysiological oscillations in the theta frequency range is said to contribute to item encoding and retrieval during spatial navigation. Although well-studied in non-human animals, this mechanism is poorly understood in humans. Previously we found that feedback stimuli presented in a virtual maze environment elicited a burst of theta power over right-posterior areas of the human scalp, and that the power and phase angle of these oscillations were greater following right turns compared to left turns in the maze. Here we investigated the source of this effect with functional magnetic resonance imaging. Consistent with our predictions, we found that 1) feedback encountered in the maze task activated right parahippocampal cortex (PHC), 2) right PHC was more activated by rewards following right turns compared to left turns in the maze, and 3) the rightward-biased activation was more pronounced in individuals who displayed good spatial abilities. These findings support our previous electrophysiological findings and highlight, in humans, a role for PHC theta oscillations in encoding salient information for the purpose of spatial navigation.
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12
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Pastötter B, Bäuml KHT. Distinct slow and fast cortical theta dynamics in episodic memory retrieval. Neuroimage 2014; 94:155-161. [DOI: 10.1016/j.neuroimage.2014.03.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 01/31/2014] [Accepted: 03/02/2014] [Indexed: 12/13/2022] Open
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13
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König SD, Buffalo EA. A nonparametric method for detecting fixations and saccades using cluster analysis: removing the need for arbitrary thresholds. J Neurosci Methods 2014; 227:121-31. [PMID: 24509130 DOI: 10.1016/j.jneumeth.2014.01.032] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Revised: 01/17/2014] [Accepted: 01/20/2014] [Indexed: 10/25/2022]
Abstract
BACKGROUND Eye tracking is an important component of many human and non-human primate behavioral experiments. As behavioral paradigms have become more complex, including unconstrained viewing of natural images, eye movements measured in these paradigms have become more variable and complex as well. Accordingly, the common practice of using acceleration, dispersion, or velocity thresholds to segment viewing behavior into periods of fixations and saccades may be insufficient. NEW METHOD Here we propose a novel algorithm, called Cluster Fix, which uses k-means cluster analysis to take advantage of the qualitative differences between fixations and saccades. The algorithm finds natural divisions in 4 state space parameters-distance, velocity, acceleration, and angular velocity-to separate scan paths into periods of fixations and saccades. The number and size of clusters adjusts to the variability of individual scan paths. RESULTS Cluster Fix can detect small saccades that were often indistinguishable from noisy fixations. Local analysis of fixations helped determine the transition times between fixations and saccades. COMPARISON WITH EXISTING METHODS Because Cluster Fix detects natural divisions in the data, predefined thresholds are not needed. CONCLUSIONS A major advantage of Cluster Fix is the ability to precisely identify the beginning and end of saccades, which is essential for studying neural activity that is modulated by or time-locked to saccades. Our data suggest that Cluster Fix is more sensitive than threshold-based algorithms but comes at the cost of an increase in computational time.
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Affiliation(s)
- Seth D König
- Wallace H. Coulter Department of Biomedical Engineering at the Georgia Institute of Technology and Emory University, 313 Ferst Drive, Atlanta, GA 30332, USA; Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, GA 30329, USA; Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, WA 98195, USA
| | - Elizabeth A Buffalo
- Yerkes National Primate Research Center, 954 Gatewood Road, Atlanta, GA 30329, USA; Department of Neurology, Emory University School of Medicine, 1440 Clifton Road, Atlanta, GA 30322, USA; Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, USA.
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