Inhibition of return and the human frontal eye fields

Intracortical recordings reveal vision-to-action cortical gradients driving human exogenous attention

Exogenous attention, the process that makes external salient stimuli pop-out of a visual scene, is essential for survival. How attention-capturing events modulate human brain processing remains unclear. Here we show how the psychological construct of exogenous attention gradually emerges over large-scale gradients in the human cortex, by analyzing activity from 1,403 intracortical contacts implanted in 28 individuals, while they performed an exogenous attention task. The timing, location and task-relevance of attentional events defined a spatiotemporal gradient of three neural clusters, which mapped onto cortical gradients and presented a hierarchy of timescales. Visual attributes modulated neural activity at one end of the gradient, while at the other end it reflected the upcoming response timing, with attentional effects occurring at the intersection of visual and response signals. These findings challenge multi-step models of attention, and suggest that frontoparietal networks, which process sequential stimuli as separate events sharing the same location, drive exogenous attention phenomena such as inhibition of return.

The role of primary motor cortex in manual inhibition of return: A transcranial magnetic stimulation study

Inhibition of return (IOR) is a behavioural phenomenon characterised by longer response times (RTs) to stimuli presented at previously cued versus uncued locations. The neural mechanisms underlying IOR effects are not fully understood. Previous neurophysiological studies have identified a role of frontoparietal areas including posterior parietal cortex (PPC) in the generation of IOR, but the contribution of primary motor cortex (M1) has not been directly tested. The present study investigated the effects of single-pulse transcranial magnetic stimulation (TMS) over M1 on manual IOR in a key-press task where peripheral (left or right) targets followed a cue at the same or opposite location at different SOAs (100/300/600/1000 ms). In Experiment 1, TMS was applied over right M1 on a randomized 50% of trials. In Experiment 2, active or sham stimulation was provided in separate blocks. In the absence of TMS (non-TMS trials in Experiment 1 and sham trials in Experiment 2), evidence of IOR was observed in RTs at longer SOAs. In both experiments, IOR effects differed between TMS and non-TMS/sham conditions, but the effects of TMS were greater and statistically significant in Experiment 1 where TMS and non-TMS trials were randomly interspersed. The magnitude of motor-evoked potentials was not altered by the cue-target relationship in either experiment. These findings do not support a key role of M1 in the mechanisms of IOR but suggest the need for further research to elucidate the role of the motor system in manual IOR effects.

Pre-saccadic attention relies more on suppression than does covert attention

During covert and pre-saccadic attentional shifts, it is unclear how facilitation and suppression processes interact for target selection. A recent countermanding task pointed to greater suppression at unattended locations during trials with saccades compared to trials without saccades (i.e., fixation and successful stop trials), whereas target facilitation did not differ. It is unknown whether this finding is restricted to countermanding paradigms that involve inhibitory processes. To test this, we adapted Gaspelin and colleagues (2015)'s attention capture task where, within the same block, one location was primed with frequent line discrimination trials, and all locations were occasionally probed using letters report trials. Participants also performed a baseline condition without priming. We tested 15 participants and examined how performance at non-primed locations was affected by covert versus pre-saccadic attention in blocks of four or six items, as well as by position from the primed location and timing from saccade onset. For both attention conditions, letter report at non-primed locations was worse compared to baseline, demonstrating suppression, and letter report at primed location was better, demonstrating facilitation. In saccades trials, letter report was better at primed locations and worse at non-primed locations compared to fixation trials. The timing of this additional pre-saccadic suppression differed from saccadic suppression. In both attention conditions, suppression was greater when primed and non-primed locations were within the same hemifield or in diagonal opposite quadrants. These results confirmed that attention preceding saccade execution suppressed non-primed locations to a larger extent than covert attention, with the same spatial quadrant effect.

The role of the parietal cortex in inhibitory processing in the vertical meridian: Evidence from elderly brain damaged patients

We explored the effects of parietal damage on inhibitory effects of visuospatial attention, inhibition of return (IOR) and inhibitory tagging (IT), in the vertical meridian. We combined a vertical spatial cue paradigm with a Stroop task employing three different temporal intervals between the spatial cue and the target (700, 1200 and 2000 ms) in two groups of patients, one with damage to the parietal cortex and underlying white matter (the parietal patients group) and the other with damage in other brain areas not including the parietal lobe (the control patient group), and a healthy control group. Healthy controls showed the expected inhibitory effects, IOR at the 700 and 1200 intervals and IT at the 1200 interval (as evidenced in a reduction in the magnitude of Stroop interference at the cued location). On the other hand, only the group of parietal patients showed delayed onset of inhibitory effects, IOR and IT appeared at the 1200 ms and 2000 ms intervals, respectively. These findings provide evidence for a role of the parietal cortex, and the underlying fibre tracts, in inhibitory processing in the vertical meridian, with damage to the parietal cortex altering the time course of attention-dependent inhibition.

Delayed Onset of Inhibition of Return in Visual Snow Syndrome

Visual snow syndrome (VSS) is a complex, sensory processing disorder. We have previously shown that visual processing changes manifest in significantly faster eye movements toward a suddenly appearing visual stimulus and difficulty inhibiting an eye movement toward a non-target visual stimulus. We propose that these changes reflect poor attentional control and occur whether attention is directed exogenously by a suddenly appearing event, or endogenously as a function of manipulating expectation surrounding an upcoming event. Irrespective of how attention is captured, competing facilitatory and inhibitory processes prioritise sensory information that is important to us, filtering out that which is irrelevant. A well-known feature of this conflict is the alteration to behaviour that accompanies variation in the temporal relationship between competing sensory events that manipulate facilitatory and inhibitory processes. A classic example of this is the “Inhibition of Return” (IOR) phenomenon that describes the relative slowing of a response to a validly cued location compared to invalidly cued location with longer cue/target intervals. This study explored temporal changes in the allocation of attention using an ocular motor version of Posner's IOR paradigm, manipulating attention exogenously by varying the temporal relationship between a non-predictive visual cue and target stimulus. Forty participants with VSS (20 with migraine) and 20 controls participated. Saccades were generated to both validly cued and invalidly cued targets with 67, 150, 300, and 500 ms cue/target intervals. VSS participants demonstrated delayed onset of IOR. Unlike controls, who exhibited IOR with 300 and 500 ms cue/target intervals, VSS participants only exhibited IOR with 500 ms cue/target intervals. These findings provide further evidence that attention is impacted in VSS, manifesting in a distinct saccadic behavioural profile, and delayed onset of IOR. Whether IOR is perceived as the build-up of an inhibitory bias against returning attention to an already inspected location or a consequence of a stronger attentional orienting response elicited by the cue, our results are consistent with the proposal that in VSS, a shift of attention elicits a stronger increase in saccade-related activity than healthy controls. This work provides a more refined saccadic behavioural profile of VSS that can be interrogated further using sophisticated neuroimaging techniques and may, in combination with other saccadic markers, be used to monitor the efficacy of any future treatments.

Time course of the inhibitory tagging effect in ongoing emotional processing. A HD-tDCS study

When a cueing procedure that usually triggers inhibition of return (IOR) effects is combined with tasks that tap semantic processing, or involve response-based conflict, an inhibitory tagging (IT) emerges that disrupts responses to stimuli at inhibited locations. IT seems to involve the executive prefrontal cortex, mainly the left dorsolateral prefrontal cortex (DLPFC), in cognitive conflict tasks. Contrary to other inhibitory effects, IT has been observed with rather short intervals, concretely when the stimulus onset asynchrony (SOA) between the prime presented at the cued location, and the subsequent target is 250 ms. Here we asked whether IT is also applied to ongoing emotional processing, and whether the left DLPFC plays a causal role in IT using HD-tDCS. In two experiments with an emotional conflict task, we observed reduced conflict effects, the signature of IT, when the prime word was presented at the cued location, and once again when the prime-target SOA was just 250 ms. Also, the IT effect was eliminated when cathodal stimulation was applied to the left DLPFC. These findings suggest that the IT effect involves areas of the executive attention network and cooperates with IOR to favor attentional allocation to novel unexplored objects/locations, irrespective of their emotional content.

What Neuroscientific Studies Tell Us about Inhibition of Return

An inhibitory aftermath of orienting, inhibition of return (IOR), has intrigued scholars since its discovery about 40 years ago. Since then, the phenomenon has been subjected to a wide range of neuroscientific methods and the results of these are reviewed in this paper. These include direct manipulations of brain structures (which occur naturally in brain damage and disease or experimentally as in TMS and lesion studies) and measurements of brain activity (in humans using EEG and fMRI and in animals using single unit recording). A variety of less direct methods (e.g., computational modeling, developmental studies, etc.) have also been used. The findings from this wide range of methods support the critical role of subcortical and cortical oculomotor pathways in the generation and nature of IOR.

The puzzle of spontaneous alternation and inhibition of return: How they might fit together

Two isolated spatial phenomena share a similar "been there; done that" effect on spatial behavior. Originally discovered in rodent learning experiments, spontaneous alternation is a tendency for the organism to visit a different arm in a T-maze on subsequent trials. Originally discovered in human studies of attention, inhibition of return is a tendency for the organism to orient away from a previously attended location. Whereas spontaneous alternation was identified by O'Keefe & Nadel as dependent on an intact hippocampus, inhibition of return is dependent on neural structures that participate in oculomotor control (the superior colliculus, parietal and frontal cortex). Despite the isolated literatures, each phenomenon has been assumed to reflect a basic novelty-seeking process, avoiding places previously visited or locations attended. In this commentary, we explore and compare the behavioral manifestations and neural underpinnings of these two phenomena, and suggest what is still needed to determine whether they operate in parallel or serial.

Top-down and bottom-up attention cause the ventriloquism effect with distinct electroencephalography modulations

The ventriloquism effect is a critical phenomenon for understanding the underlying mechanisms of multisensory integration. Cross-modal spatial attention causes a distortion of sound localization, although the neural basis of the effect remains an unanswered question. We hypothesized that top-down and bottom-up visual-spatial attention causes the ventriloquism effect with different modulations of ongoing neural oscillation. To test this hypothesis, human scalp electroencephalography (EEG) was measured during a sound localization task. Top-down attention suppressed the EEG amplitude in the alpha frequency (10 Hz) over the contralateral temporal electrode sites to visual cue hemifields. Bottom-up attention shifted the EEG phase to the theta frequency (7 Hz), rather than suppressing the amplitude. Two different neural mechanisms of ongoing neural oscillation contributed toward the ventriloquism effect, with different spatial attention.

Neural field model of memory-guided search

Many organisms can remember locations they have previously visited during a search. Visual search experiments have shown exploration is guided away from these locations, reducing redundancies in the search path before finding a hidden target. We develop and analyze a two-layer neural field model that encodes positional information during a search task. A position-encoding layer sustains a bump attractor corresponding to the searching agent's current location, and search is modeled by velocity input that propagates the bump. A memory layer sustains persistent activity bounded by a wave front, whose edges expand in response to excitatory input from the position layer. Search can then be biased in response to remembered locations, influencing velocity inputs to the position layer. Asymptotic techniques are used to reduce the dynamics of our model to a low-dimensional system of equations that track the bump position and front boundary. Performance is compared for different target-finding tasks.

Temporal dynamics of saccades explained by a self-paced process

Sensory organs are thought to sample the environment rhythmically thereby providing periodic perceptual input. Whisking and sniffing are governed by oscillators which impose rhythms on the motor-control of sensory acquisition and consequently on sensory input. Saccadic eye movements are the main visual sampling mechanism in primates, and were suggested to constitute part of such a rhythmic exploration system. In this study we characterized saccadic rhythmicity, and examined whether it is consistent with autonomous oscillatory generator or with self-paced generation. Eye movements were tracked while observers were either free-viewing a movie or fixating a static stimulus. We inspected the temporal dynamics of exploratory and fixational saccades and quantified their first-order and high-order dependencies. Data were analyzed using methods derived from spike-train analysis, and tested against mathematical models and simulations. The findings show that saccade timings are explained by first-order dependencies, specifically by their refractory period. Saccade-timings are inconsistent with an autonomous pace-maker but are consistent with a "self-paced" generator, where each saccade is a link in a chain of neural processes that depend on the outcome of the saccade itself. We propose a mathematical model parsimoniously capturing various facets of saccade-timings, and suggest a possible neural mechanism producing the observed dynamics.

Functional connectivity between prefrontal and parietal cortex drives visuo-spatial attention shifts

It is well established that the frontal eye-fields (FEF) in the dorsal attention network (DAN) guide top-down selective attention. In addition, converging evidence implies a causal role for the FEF in attention shifting, which is also known to recruit the ventral attention network (VAN) and fronto-striatal regions. To investigate the causal influence of the FEF as (part of) a central hub between these networks, we applied thetaburst transcranial magnetic stimulation (TBS) off-line, combined with functional magnetic resonance (fMRI) during a cued visuo-spatial attention shifting paradigm.

We found that TBS over the right FEF impaired performance on a visual discrimination task in both hemifields following attention shifts, while only left hemifield performance was affected when participants were cued to maintain the focus of attention. These effects recovered ca. 20 min post stimulation. Furthermore, particularly following attention shifts, TBS suppressed the neural signal in bilateral FEF, right inferior and superior parietal lobule (IPL/SPL) and bilateral supramarginal gyri (SMG). Immediately post stimulation, functional connectivity was impaired between right FEF and right SMG as well as right putamen. Importantly, the extent of decreased connectivity between right FEF and right SMG correlated with behavioural impairment following attention shifts.

The main finding of this study demonstrates that influences from right FEF on SMG in the ventral attention network causally underly attention shifts, presumably by enabling disengagement from the current focus of attention.

•

Thetaburst stimulation to the right FEF temporarily impairs bilateral attention shifts.

•

Lateralised behavioural deficits in the contralateral hemifield are observed when cued to maintain attention.

•

These effects recover ca. 20 min post stimulation.

•

During shifts, neural activity is suppressed following right FEF TBS in the dorsal attention network and supramarginal gyri.

•

Influences from right FEF to SMG causally underlie attention shifts, presumably by enabling disengagement from current focus.

Stimulus-Locked and Response-Locked ERP Correlates of Spatial Inhibition of Return (IOR) in Old Age

Behavioral research has shown that Inhibition of Return (IOR) is preserved in old age although at longer time intervals between cue and target, which has been interpreted as reflecting a later disengagement from the cue. A recent event-related potential (ERP) study attributed this age-related pattern to an enhanced processing of the cue. Previous ERP research in young samples indicates that target and response processing are also affected by IOR, which makes interesting to study the ERP correlates of IOR from cue presentation to response execution. In this regard, in the present study stimulus-locked (cue-locked and target-locked) and response-locked ERPs were explored in healthy young and older participants. The behavioral results indicated preserved IOR in the older participants. The cue-locked ERPs could suggest that the older participants processed the cue as a warning signal to prepare for the upcoming target stimulus. Under IOR, target-locked ERPs of both age groups showed lower N1 amplitudes suggesting a suppression/inhibition of cued targets. During the P3 rising period, in young subjects a negative shift (Nd effect) to cued targets was observed in the lower visual field (LVF), and a positive shift (Pd effect) in the upper visual field. However, in the older group the Nd effect was absent suggesting a reduction of attentional resolution in the LVF. The older group showed enhanced motor activation to prepare correct responses, although IOR effects on response-locked lateralized readiness potential LRP indicated reduced response preparation to cued targets in both age groups. In general, results suggest that the older adults inhibit or reduce the visual processing of targets appearing at cued locations, and the preparation to respond to them, but with the added cost of allocating more attentional resources onto the cue and of maintaining a more effortful processing during the sequence of stimuli within the trial.

Frontal eye field, where art thou? Anatomy, function, and non-invasive manipulation of frontal regions involved in eye movements and associated cognitive operations

The planning, control and execution of eye movements in 3D space relies on a distributed system of cortical and subcortical brain regions. Within this network, the Eye Fields have been described in animals as cortical regions in which electrical stimulation is able to trigger eye movements and influence their latency or accuracy. This review focuses on the Frontal Eye Field (FEF) a “hub” region located in Humans in the vicinity of the pre-central sulcus and the dorsal-most portion of the superior frontal sulcus. The straightforward localization of the FEF through electrical stimulation in animals is difficult to translate to the healthy human brain, particularly with non-invasive neuroimaging techniques. Hence, in the first part of this review, we describe attempts made to characterize the anatomical localization of this area in the human brain. The outcome of functional Magnetic Resonance Imaging (fMRI), Magneto-encephalography (MEG) and particularly, non-invasive mapping methods such a Transcranial Magnetic Stimulation (TMS) are described and the variability of FEF localization across individuals and mapping techniques are discussed. In the second part of this review, we will address the role of the FEF. We explore its involvement both in the physiology of fixation, saccade, pursuit, and vergence movements and in associated cognitive processes such as attentional orienting, visual awareness and perceptual modulation. Finally in the third part, we review recent evidence suggesting the high level of malleability and plasticity of these regions and associated networks to non-invasive stimulation. The exploratory, diagnostic, and therapeutic interest of such interventions for the modulation and improvement of perception in 3D space are discussed.

Relating dopaminergic and cholinergic polymorphisms to spatial attention in infancy

Early selective attention skills are a crucial building block for cognitive development, as attention orienting serves as a primary means by which infants interact with and learn from the environment. Although several studies have examined infants' attention orienting using the spatial cueing task, relatively few studies have examined neurodevelopmental factors associated with attention orienting during infancy. The present study examined the relationship between normative genetic polymorphisms affecting dopamine and acetylcholine signaling and attention orienting in 7-month-old infants during a spatial cueing task. We focused on 3 genes, including the CHRNA4 C¹⁵⁴⁵T SNP (rs10344946), DAT1 3'UTR VNTR, and COMT Val¹⁵⁸Met SNP (rs4680), as previous adult research has linked spatial attention skills to these polymorphisms. Behavioral measures included both facilitation of orienting at the cued location as well as inhibition of return (IOR), in which attention orienting is suppressed at the cued location. Results indicated that COMT Val carriers showed robust IOR relative to infants with the Met/Met genotype. However, COMT was unrelated to infants' facilitation responses, and there were no effects of CHRNA4 or DAT1 on either facilitation or IOR. Overall, this study suggests that variations in dopamine signaling, likely in prefrontal cortex, contribute to individual differences in orienting during early development.

Hemispheric differences in the voluntary control of spatial attention: direct evidence for a right-hemispheric dominance within frontal cortex

Lesion studies in neglect patients have inspired two competing models of spatial attention control, namely, Heilman's "hemispatial" theory and Kinsbourne's "opponent processor" model. Both assume a functional asymmetry between the two hemispheres but propose very different mechanisms. Neuroimaging studies have identified a bilateral dorsal frontoparietal network underlying voluntary shifts of spatial attention. However, lateralization of attentional processes within this network has not been consistently reported. In the current study, we aimed to provide direct evidence concerning the functional asymmetry of the right and left FEF during voluntary shifts of spatial attention. To this end, we applied fMRI-guided neuronavigation to disrupt individual FEF activation foci with a longer-lasting inhibitory patterned TMS protocol followed by a spatial cueing task. Our results indicate that right FEF stimulation impaired the ability of shifting spatial attention toward both hemifields, whereas the effects of left FEF stimulation were limited to the contralateral hemifield. These results provide strong direct evidence for right-hemispheric dominance in spatial attention within frontal cortex supporting Heilman's "hemispatial" theory. This complements previous TMS studies that generally conform to Kinsbourne's "opponent processor" model after disruption of parietal cortex, and we therefore propose that both theories are not mutually exclusive.

fMRI correlates of inhibition of return in perifoveal and peripheral visual field

When a target appears in the same peripheral location as a previous cue, responding is typically delayed if the cue-target interval is relatively long. This phenomenon is termed inhibition of return (IOR) and has been suggested to reflect an attentional bias in favour of novel visual space. It has been demonstrated recently that IOR is much stronger in the far periphery than in the perifoveal visual field. The present study further investigated the neural mechanisms underlying this eccentricity effect of IOR with an event-related fMRI technique. The results demonstrated a stronger activation in visual cortex for perifoveal processing and a broader activation in multiple brain areas for peripheral processing. When IOR effects were compared between these two areas, a stronger activation of the fronto-parietal network was evidenced for perifoveal versus peripheral IOR, while the prefrontal cortex was more strongly involved in the peripheral IOR versus perifoveal IOR. These results suggest that different neural mechanisms are mediating the dissociable inhibitory functions between the perifoveal and peripheral visual field.

Inhibition of return in the visual field: the eccentricity effect is independent of cortical magnification

Inhibition of return (IOR) as an indicator of attentional control is characterized by an eccentricity effect, that is, the more peripheral visual field shows a stronger IOR magnitude relative to the perifoveal visual field. However, it could be argued that this eccentricity effect may not be an attention effect, but due to cortical magnification. To test this possibility, we examined this eccentricity effect in two conditions: the same-size condition in which identical stimuli were used at different eccentricities, and the size-scaling condition in which stimuli were scaled according to the cortical magnification factor (M-scaling), thus stimuli being larger at the more peripheral locations. The results showed that the magnitude of IOR was significantly stronger in the peripheral relative to the perifoveal visual field, and this eccentricity effect was independent of the manipulation of stimulus size (same-size or size-scaling). These results suggest a robust eccentricity effect of IOR which cannot be eliminated by M-scaling. Underlying neural mechanisms of the eccentricity effect of IOR are discussed with respect to both cortical and subcortical structures mediating attentional control in the perifoveal and peripheral visual field.

Frontal non-invasive neurostimulation modulates antisaccade preparation in non-human primates

A combination of oculometric measurements, invasive electrophysiological recordings and microstimulation have proven instrumental to study the role of the Frontal Eye Field (FEF) in saccadic activity. We hereby gauged the ability of a non-invasive neurostimulation technology, Transcranial Magnetic Stimulation (TMS), to causally interfere with frontal activity in two macaque rhesus monkeys trained to perform a saccadic antisaccade task. We show that online single pulse TMS significantly modulated antisaccade latencies. Such effects proved dependent on TMS site (effects on FEF but not on an actively stimulated control site), TMS modality (present under active but not sham TMS on the FEF area), TMS intensity (intensities of at least 40% of the TMS machine maximal output required), TMS timing (more robust for pulses delivered at 150 ms than at 100 post target onset) and visual hemifield (relative latency decreases mainly for ipsilateral AS). Our results demonstrate the feasibility of using TMS to causally modulate antisaccade-associated computations in the non-human primate brain and support the use of this approach in monkeys to study brain function and its non-invasive neuromodulation for exploratory and therapeutic purposes.

Cortical control of inhibition of return: evidence from patients with inferior parietal damage and visual neglect

Inhibition of return (IOR) refers to slower reaction times to targets presented at previously stimulated or inspected locations. This phenomenon biases orienting towards novel locations and is functional to an effective exploration of the environment. Patients with right brain damage and left visual neglect explore their environment asymmetrically, with strong difficulties to orient attention to left-sided objects. We show for the first time a dissociation between manual and saccadic IOR in neglect. Our patients demonstrated facilitation, instead of inhibition, for repeated right-sided targets with manual responses, but normal IOR to right-sided targets with saccadic responses. All neglect patients had damage to the supramarginal gyrus in the right parietal lobe, or to its connections with the ipsilateral prefrontal cortex. We concluded that IOR with manual responses relies on fronto-parietal attentional networks in the right hemisphere, whose functioning is typically impaired in neglect patients. Saccadic IOR may instead depend on circuits less likely to be damaged in neglect, such as the retinotectal visual pathway.

Inhibitory Control and the Frontal Eye Fields

Inhibitory control mechanisms are important in a range of behaviors to prevent execution of motor acts which, having been planned, are no longer necessary. Ready examples of this can be seen in a range of sports, such as cricket and baseball, where the choice between execution or inhibition of a bat swing must be made in a brief time interval. The role of the FEFs, an area typically described in relation to eye movement functions but also involved in visual processes, was investigated in an inhibitory control task using transcranial magnetic stimulation (TMS). A stop signal task with manual responses was used, providing measures of impulsivity and inhibitory control. TMS over FEF had no effect on response generation (impulsivity, indexed by go signal RT) but disrupted inhibitory control (indexed by stop signal RT). This is the first demonstration of a role for FEF in this type of task in normal subjects in a task which did not require eye movements and complements previous TMS findings of roles for pre-SMA and inferior frontal gyrus (IFG) in inhibitory control.

Repetitive transcranial magnetic stimulation over frontal eye fields disrupts visually cued auditory attention

Voluntary eye movements and covert shifts of visual attention activate the same brain regions. Specifically, the intraparietal sulcus and the frontal eye fields (FEF) appear to be involved both with generating voluntary saccades as well with attending to a peripheral spatial location. Furthermore, these regions appear to be required by both tasks--functional disruption of these regions impairs both tasks. Therefore, it appears that the targeting system that allows us to plan saccades is the same system that allows us to covertly track peripheral visual information. Recent neuroimaging studies suggest that these brain regions are also activated when participants engage in auditory spatial attention tasks. However, it remains unclear whether these regions are required by these tasks. We used repetitive transcranial magnetic stimulation (rTMS) to disrupt the FEF while participants performed an auditory localization task. On each trial, a visual cue directed attention to the probable laterality of the auditory target, and the participant decided whether the subsequent target sound came from an upper or lower speaker. In the absence of TMS, individuals were faster to respond to targets that occurred on the cued side (valid trials) than when the target appears contralaterally to the cued side (invalid side). TMS interfered with this effect, such that the costs associated with ipsilateral invalidly cued targets were substantially reduced. These results suggest that the eye-movement system is needed for normal auditory attention.

Dopaminergic Control of Attentional Flexibility: Inhibition of Return is Associated with the Dopamine Transporter Gene (DAT1)

Genetic variability related to the dopamine (DA) transporter gene (DAT1) has received increasing attention as a possible modulator of human cognition. The 9-repeat allele of the DAT1 gene is presumably associated with higher striatal DA levels than the 10-repeat allele, which might support inhibitory control functions. We investigated the impact of the DAT1 gene on the inhibition of return (IOR) effect, which refers to the fact that people are slower to detect a target if it appears in a previously attended location. 140 healthy adults, genotyped for the DAT1 gene, performed an IOR task with stimulus-onset asynchronies (SOAs) between attention cue and target of 150–1200 ms. Nine-repeat carriers showed more pronounced IOR effect than 10/10 homozygous at short SOAs but both groups of subjects eventually reached the same magnitude of IOR. Our findings support the idea that striatal DA levels promote IOR, presumably by biasing the interplay between prefrontal and striatal networks towards greater cognitive flexibility.

Contribution of the superior colliculi to post-stroke unilateral spatial neglect and recovery

Unilateral spatial neglect (USN) is a highly prevalent and disabling consequence of stroke that often responds poorly to existing interventions. Its underlying neural mechanisms are still unclear. Recent work suggests that post-stroke USN may be partly related to a disruption of top-down and bottom-up control of visual attention mediated in part through the midbrain superior colliculi (SC). With mounting evidence from animal and human research, our objectives were: (1) to synthesize the literature implicating the SC in USN; (2) to review the rationale and potential for using eye patching and prism adaptation as USN treatment approaches that recruit SC involvement; and (3) to provide recommendations for research on the potential of therapeutic interventions that involve and/or target the retino-collicular pathway. Given the paucity of human studies, the contribution of the SC in USN, while plausible, remains to be confirmed. Further exploration of the mechanisms involved and their impact on USN in human subjects will help develop theoretically based intervention strategies tailored to USN type.

Influence of environmental statistics on inhibition of saccadic return

Initiating an eye movement is slowed if the saccade is directed to a location that has been fixated in the recent past. We show that this inhibitory effect is modulated by the temporal statistics of the environment: If a return location is likely to become behaviorally relevant, inhibition of return is absent. By fitting an accumulator model of saccadic decision-making, we show that the inhibitory effect and the sensitivity to local statistics can be dissociated in their effects on the rate of accumulation of evidence, and the threshold controlling the amount of evidence needed to generate a saccade.

An intact eye-movement system is not required to generate inhibition of return

AI is unable to make eye-movements and has a deficit of reflexive attention. Here, we demonstrate that despite these deficits AI exhibits inhibition of return (IOR) for peripherally cued objects and locations. These data suggest that an intact oculomotor system is not required for the generation of either object-based or location-based IOR and are consistent with the view that the early, facilitatory effects of peripheral cues and late IOR effects are mediated by different mechanisms.

Inhibitory deficits in children with attention-deficit/hyperactivity disorder: intentional versus automatic mechanisms of attention

Application of theoretically based tasks to the study of the development of selective attention has led to intriguing new findings concerning the role of inhibitory mechanisms. This study examined inhibitory mechanisms using a countermanding task and an inhibition of return task to compare deficits in intentionally, versus reflexively, controlled inhibition of attention in children with attention deficit hyperactivity disorder. Fifty children with attention-deficit/hyperactivity disorder (ADHD) were classified into one of three subtypes: predominantly inattentive (ADHD/PI), combined (ADHD/C), and those children with ADHD/C who also met criteria for comorbid oppositional defiant disorder (ADHD/C + ODD). The groups were compared to a comparison group of children (n = 21). The countermanding task showed that the ADHD groups required more time to inhibit responses and this impairment did not differ among subtypes. With respect to reflexively controlled inhibition, compared with controls ADHD/C and ADHD/C + ODD groups showed impaired reflexive inhibition, whereas the ADHD/PI group was considerably less impaired. The findings highlight a dissociation between the two forms of inhibitory deficits among children with the inattentive subtype, and raise the possibility that the efficient operation of reflexive inhibitory mechanisms might be necessary for the development of effective intentional control of inhibition.

Neuronal modulation of auditory attention by informative and uninformative spatial cues

Sounds provide important information about the spatial environment, including the location of approaching objects. Attention to sounds can be directed through automatic or more controlled processes, which have been well studied in the visual modality. However, little is known about the neural underpinnings of attentional control mechanisms for auditory signals. We studied healthy adults who underwent event-related FMRI while performing a task that manipulated automatic and more controlled auditory orienting by varying the probability that cues correctly predicted target location. Specifically, we examined the effects of uninformative (50% validity ratio) and informative (75% validity ratio) auditory cues on reaction time (RT) and neuronal functioning. The stimulus-onset asynchrony (SOA) between the cue and the target was either 100 or 800 ms. At the 100 ms SOA, RT was faster for valid than invalid trials for both cue types, and frontoparietal activation was greater for invalid than valid trials. At the 800 ms SOA, RT and functional activation depended on whether cues were informative or uninformative, and whether cues correctly or incorrectly predicted the target location. Contrary to our prediction, activation in a frontoparietal network was greater for uninformative than informative cues across several different comparisons and at both SOAs. This finding contrasts with similar research of visual orienting, and suggests that the auditory modality may be more biased toward automatic shifts of attention following uninformative cues.

Evidence for an attentional component in saccadic inhibition of return

After presentation of a peripheral cue, facilitation at the cued location is followed by inhibition of return (IOR). It has been recently proposed that IOR may originate at different processing stages for manual and ocular responses, with manual IOR resulting from inhibited attentional orienting, and ocular IOR resulting form inhibited motor preparation. Contrary to this interpretation, we found an effect of target contrast on saccadic IOR. The effect of contrast decreased with increasing reaction times (RTs) for saccades, but not for manual key-press responses. This may have masked the effect of contrast on IOR with saccades in previous studies (Hunt and Kingstone in J Exp Psychol Hum Percept Perform 29:1068-1074, 2003) because only mean RTs were considered. We also found that background luminance strongly influenced the effects of gap and target contrast on IOR.

Equivalent charge source model based iterative maximum neighbor weight for sparse EEG source localization

How to localize the neural electric activities within brain effectively and precisely from the scalp electroencephalogram (EEG) recordings is a critical issue for current study in clinical neurology and cognitive neuroscience. In this paper, based on the charge source model and the iterative re-weighted strategy, proposed is a new maximum neighbor weight based iterative sparse source imaging method, termed as CMOSS (Charge source model based Maximum neighbOr weight Sparse Solution). Different from the weight used in focal underdetermined system solver (FOCUSS) where the weight for each point in the discrete solution space is independently updated in iterations, the new designed weight for each point in each iteration is determined by the source solution of the last iteration at both the point and its neighbors. Using such a new weight, the next iteration may have a bigger chance to rectify the local source location bias existed in the previous iteration solution. The simulation studies with comparison to FOCUSS and LORETA for various source configurations were conducted on a realistic 3-shell head model, and the results confirmed the validation of CMOSS for sparse EEG source localization. Finally, CMOSS was applied to localize sources elicited in a visual stimuli experiment, and the result was consistent with those source areas involved in visual processing reported in previous studies.

Two orienting mechanisms in posterior parietal lobule: an rTMS study of the Simon and SNARC effects

The aim of the present study was to investigate, with repetitive transcranial magnetic stimulation (rTMS), the involvement of posterior parietal lobule (PPL) circuits in producing the Simon effect and the spatial-numerical association of response codes (SNARC) effect. The Simon effect is indexed by faster responses to left-side stimuli with left- than with right-side key-presses and faster responses to right-side stimuli with right- than with left-side key-presses. The SNARC effect is indexed by faster responses to smaller numbers with left- than with right-side key-presses and faster responses to larger numbers with right- than with left-side key-presses. Participants were required to perform a parity judgement on numbers ranging from 1 to 9 (without 5), by pressing a left or a right response key. The numbers were presented to either the left or the right side of fixation. Two bilateral PPL areas lying along the intraparietal sulcus (IPS) were stimulated with rTMS. Results suggested a causal role of the anterior portion of PPL of both hemispheres in the Simon effect and of the posterior portion of PPL of both hemispheres in the Simon effect and the SNARC effect.

Covert orienting of attention and overt eye movements activate identical brain regions

This study investigated the anatomical relationship between covert and overt shifts of attention. Previous studies have found that the areas of the brain activated by covert and overt shifts of attention are very similar. However, despite a general agreement between studies there are a few issues that merit closer inspection. Primarily, the tasks aiming to produce covert or overt shifts of attention were not always comparable. Secondly, the previous studies disagreed on whether greater neural activity is elicited by covert shifts or overt shifts of attention. Thirdly, the previous studies differed on whether the shifts of attention were exogenously or endogenously driven. Finally, the statistical analyses used by all previous studies failed to account for between subject variability. The present study was designed to address all these issues. Twelve healthy subjects performed either covert or overt shifts of attention while the functional magnetic resonance imaging (fMRI) signal was continuously measured. In line with the previous studies, the present study showed a virtually complete overlap between areas of the brain recruited during covert shifts of attention and areas of the brain recruited during overt shifts of attention. Furthermore, using endogenously driven shifts of attention this study found that overt shifts of attention resulted in higher levels of activation in the brain than covert shifts of attention. The results of this study provide support for the premotor theory of attention that posits that the attentional and motor systems are the result of neural activation in the same areas of the brain.

Inhibition of Return Arises from Inhibition of Response Processes: An Analysis of Oscillatory Beta Activity

In the orienting of attention paradigm, inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. No consensus has yet been reached regarding the stages of information processing underlying the inhibition. We report the results of an electro-encephalogram experiment designed to examine the involvement of response inhibition in IOR. Using a cue-target design and a target-target design, we addressed the role of response inhibition in a location discrimination task. Event-related changes in beta power were measured because oscillatory beta activity has been shown to be related to motor activity. Bilaterally located sources in the primary motor cortex showed event-related beta desynchronization (ERD) both at cue and target presentation and a rebound to event-related beta synchronization (ERS) after movement execution. In both designs, IOR arose from an enhancement of beta synchrony. IOR was related to an increase of beta ERS in the target-target design and to a decrease of beta ERD in the cue-target design. These results suggest an important role of response inhibition in IOR.

Lp norm iterative sparse solution for EEG source Localization

How to localize the neural electric activities effectively and precisely from the scalp EEG recordings is a critical issue for clinical neurology and cognitive neuroscience. In this paper, based on the spatial sparse assumption of brain activities, proposed is a novel iterative EEG source imaging algorithm, Lp norm iterative sparse solution (LPISS). In LPISS, the lp (p < or =1) norm constraint for sparse solution is integrated into the iterative weighted minimum norm solution of the underdetermined EEG inverse problem, and it is the constraint and the iteratively renewed weight that forces the inverse problem to converge to a sparse solution effectively. The conducted simulation studies with comparison to LORETA and FOCUSS for various dipoles configurations confirmed the validation of LPISS for sparse EEG source localization. Finally, LPISS was applied to a real evoked potential collected in a study of inhibition of return (IOR), and the result was consistent with the previously suggested activated areas involved in an IOR process.

[Inhibition of return in schizophrenia: a review]

INTRODUCTION

Most visual environments contain more information than the human brain can process in real time. To overcome this limitation, the attention system acts as a filter by selectively orienting attention to specific regions of the visual field. This ability to orient attention can be reflected in covert shift processes of attention.

LITERATURE FINDINGS

In a typical covert orienting task, subjects have to maintain fixation on a central cross and respond as quickly as possible to a target, which appears in a peripheral box following a cue that summons attention to the direction where the target is going to appear (valid cueing) or to the contralateral direction (invalid cueing). When the cues are nonpredictive, the response characteristics critically depend on stimulus-onset asynchrony (SOA). With short SOAs (<300ms), valid cues result in a reaction time advantage over invalid trials, which is due to a reflexive shift of attention towards the source of stimulation. In contrast, with longer SOAs, valid cues result in longer reaction times to the subsequent target.

DISCUSSION

This phenomenon is known as the inhibition of return and is mostly thought to reflect an inhibitory mechanism protecting the organism from redirecting attention to previously scanned insignificant locations. Many studies have reported blunted or delayed inhibition of return in patients with schizophrenia. However, some authors reported normal amounts of inhibition of return. This can be partly explained by the use of manipulations of the covert orienting of the attention paradigm that is known to enhance the course of inhibition of return.

CONCLUSION

The deficit of inhibition of return seems to be time-stable and to be unrelated to psychopathology or length of illness. The contribution of neuroleptic medication to this deficit cannot be determined. Recent data suggest a deficit of inhibition of return in two human models of psychosis (dimethyltryptamine and ketamine). Further studies should clarify whether blunted inhibition of return might represent a trait marker of schizophrenia.

Gaze cueing of attention: visual attention, social cognition, and individual differences

During social interactions, people's eyes convey a wealth of information about their direction of attention and their emotional and mental states. This review aims to provide a comprehensive overview of past and current research into the perception of gaze behavior and its effect on the observer. This encompasses the perception of gaze direction and its influence on perception of the other person, as well as gaze-following behavior such as joint attention, in infant, adult, and clinical populations. Particular focus is given to the gaze-cueing paradigm that has been used to investigate the mechanisms of joint attention. The contribution of this paradigm has been significant and will likely continue to advance knowledge across diverse fields within psychology and neuroscience.

Human Frontal Eye Fields and Spatial Priming of Pop-out

“Priming of pop-out” is a form of implicit memory that facilitates detection of a recently inspected search target. Repeated presentation of a target's features or its spatial position improves detection speed (feature/spatial priming). This study investigated a role for the human frontal eye fields (FEFs) in the priming of color pop-out. To test the hypothesis that the FEFs play a role in short-term memory storage, transcranial magnetic stimulation (TMS) was applied during the intertrial interval. There was no effect of TMS on either spatial or feature priming. To test whether the FEFs are important when a saccade is being programmed to a repeated target color or location, TMS was applied during the search array. TMS over the left but not the right FEFs abolished spatial priming, but had no effect on feature priming. These findings demonstrate functional specialization of the left FEFs for spatial priming, and distinguish this role from target discrimination and saccade-related processes. The results suggest that the left FEFs integrate a spatial memory signal with an evolving saccade program, which facilitates saccades to a recently inspected location.

Temporal dynamics of the attentional spotlight: neuronal correlates of attentional capture and inhibition of return in early visual cortex

A stimulus that suddenly appears in the corner of the eye inevitably captures our attention, and this in turn leads to faster detection of a second stimulus presented at the same position shortly thereafter. After about 250 msec, however, this effect reverses and the second stimulus is detected faster when it appears far away from the first. Here, we report a potential physiological correlate of this time-dependent attentional facilitation and inhibition. We measured the activity in visual cortex representations of the second (target) stimulus' location depending on the stimulus onset asynchrony (SOA) and spatial distance that separated the target from the preceding cue stimulus. At an SOA of 100 msec, the target yielded larger responses when it was presented near to than far away from the cue. At an SOA of 850 msec, however, the response to the target was more pronounced when it appeared far away from the cue. Our data show how the neural substrate of visual orienting is guided by immediately preceding sensory experience and how a fast-reacting brain system modulates sensory processing by briefly increasing and subsequently decreasing responsiveness in parts of the visual cortex. We propose these activity modulations as the neural correlate of the sequence of perceptual facilitation and inhibition after attentional capture.