The effect of spatial and temporal information on saccades and neural activity in oculomotor structures

Positive and Negative Symptoms Are Associated with Distinct Effects on Predictive Saccades

The predictive saccade task is a motor learning paradigm requiring saccades to track a visual target moving in a predictable pattern. Previous research has explored extensively anti-saccade deficits observed across psychosis, but less is known about predictive saccade-related mechanisms. The dataset analysed came from the studies of Crawford et al, published in 1995, where neuroleptically medicated schizophrenia and bipolar affective disorder patients were compared with non-medicated patients and control participants using a predictive saccade paradigm. The participant groups consisted of medicated schizophrenia patients (n = 40), non-medicated schizophrenia patients (n = 18), medicated bipolar disorder patients (n = 14), non-medicated bipolar disorder patients (n = 18), and controls (n = 31). The current analyses explore relationships between predictive saccades and symptomatology, and the potential interaction of medication. Analyses revealed that the schizophrenia and bipolar disorder diagnostic categories are indistinguishable in patterns of predictive control across several saccadic parameters, supporting a dimensional hypothesis. Once collapsed into predominantly high-/low- negative/positive symptoms, regardless of diagnosis, differences were revealed, with significant hypometria and lower gain in those with more negative symptoms. This illustrates how the presentation of the deficits is homogeneous across diagnosis, but heterogeneous when surveyed by symptomatology; attesting that a diagnostic label is less informative than symptomatology when exploring predictive saccades.

Saccade eye movement in children with attention deficit hyperactivity disorder

Objects: This study aims to investigate the saccade/anti-saccade eye movement in children with attention deficit/hyperactivity disorder (ADHD).Methods: Twelve children (8.8 ± 0.8 years) diagnosed with ADHD (DSM-V) and 12 control (9.1 ± 0.3 years) were invited to participate in the experiment where the iView Hi-SPEED eyetracker, with the sample rate at 500 Hz Binocular, was employed. The visual guided saccade (VGS) task was used to collect saccade latency and accuracy values. The anti-saccade task was used to collect saccade latency and accuracy values as well as the percentage of direction errors (PDE).Results: Children with ADHD showed a significant difference in latency in the 7.5° target and imprecision in both targets (7.5° and 15°) during the VGS task. Moreover, the ADHD group exhibited shorter latency (15° target) and significantly higher numbers in the Percentage of Direction Errors in the anti-saccade tasks than the control group.Conclusions: The results suggest that children with ADHD have the following difficulties: precise oculomotor control, oculomotor response inhibition function and basic visual attention.

Implicit learning impairment identified via predictive saccades in Huntington's disease correlates with extended cortico-striatal atrophy

The ability to anticipate events and execute motor commands prior to a sensory event is an essential capability for human's everyday life. This implicitly learned anticipatory behavior depends on the past performance of repeated sensorimotor interactions timed with external cues. This kind of predictive behavior has been shown to be compromised in neurological disorders such as Huntington disease (HD), in which neural atrophy includes key cortical and basal ganglia regions. To investigate the neural basis of the anticipatory behavioral deficits in HD we used a predictive-saccade paradigm that requires predictive control to generate saccades in a metronomic temporal pattern. This is ideal because the integrity of the oculomotor network that includes the striatum and prefrontal, parietal, occipital and temporal cortices can be analyzed using structural MRI. Our results showed that the HD patients had severe predictive saccade deficits (i.e., an inability to reduce saccade reaction time in predictive condition), which are accentuated in patients with more severe motor deterioration. Structural imaging analyses revealed that these anticipatory deficits correlated with grey-matter atrophy in frontal, parietal-occipital and striatal regions. These findings indicate that the predictive saccade control deficits in HD are related to an extended cortico-striatal atrophy. This suggests that eye movement measurement could be a reliable marker of the progression of cognitive deficits in HD.

Neural substrates of internally-based and externally-cued timing: An activation likelihood estimation (ALE) meta-analysis of fMRI studies

A dynamic interplay exists between Internally-Based (IBT) and Externally-Cued (ECT) time processing. While IBT processes support the self-generation of context-independent temporal representations, ECT mechanisms allow constructing temporal representations primarily derived from the structure of the sensory environment. We performed an activation likelihood estimation (ALE) meta-analysis on 177 fMRI experiments, from 79 articles, to identify brain areas involved in timing; two individual ALEs tested the hypothesis of a neural segregation between IBT and ECT. The general ALE highlighted a network involving supplementary motor area (SMA), intraparietal sulcus, inferior frontal gyrus (IFG), insula (INS) and basal ganglia. We found evidence of a partial dissociation between IBT and ECT. IBT relies on a subset of areas also involved in ECT, however ECT tasks activate SMA, right IFG, left precentral gyrus and INS in a significantly stronger way. Present results suggest that ECT involves the detection of environmental temporal regularities and their integration with the output of the IBT processing, to generate a representation of time which reflects the temporal metric of the environment.

Neural correlates of proactive and reactive inhibition of saccadic eye movements

Although research on goal-directed, proactive inhibitory control (IC) and stimulus-driven, reactive IC is growing, no previous study has compared proactive IC in conditions of uncertainty with regard to upcoming inhibition to conditions of certain upcoming IC. Therefore, we investigated effects of certainty and uncertainty on behavior and blood oxygen level dependent (BOLD) signal in proactive and reactive IC. In two studies, healthy adults performed saccadic go/no-go and prosaccade/antisaccade tasks. The certainty manipulation had a highly significant behavioral effect in both studies, with inhibitory control being more successful under certain than uncertain conditions on both tasks (p ≤ 0.001). Saccadic go responses were significantly less efficient under conditions of uncertainty than certain responding (p < 0.001). Event-related functional magnetic resonance imaging (fMRI) (one study) revealed a dissociation of certainty- and uncertainty-related proactive inhibitory neural correlates in the go/no-go task, with lateral and medial prefrontal and occipital cortex showing stronger deactivations during uncertainty than during certain upcoming inhibition, and lateral parietal cortex being activated more strongly during certain upcoming inhibition than uncertainty or certain upcoming responding. In the antisaccade task, proactive BOLD effects arose due to stronger deactivations in uncertain response conditions of both tasks and before certain prosaccades than antisaccades. Reactive inhibition-related BOLD increases occurred in inferior parietal cortex and supramarginal gyrus (SMG) in the go/no-go task only. Proactive IC may imply focusing attention on the external environment for encoding salient or alerting events as well as inhibitory mechanisms that reduce potentially distracting neural processes. SMG and inferior parietal cortex may play an important role in both proactive and reactive IC of saccades.

Predictive saccades in children and adults: A combined fMRI and eye tracking study

Saccades were assessed in 21 adults (age 24 years, SD = 4) and 15 children (age 11 years, SD = 1), using combined functional magnetic resonance imaging (fMRI) and eye-tracking. Subjects visually tracked a point on a horizontal line in four conditions: time and position predictable task (PRED), position predictable (pPRED), time predictable (tPRED) and visually guided saccades (SAC). Both groups in the PRED but not in pPRED, tPRED and SAC produced predictive saccades with latency below 80 ms. In task versus group comparisons, children's showed less efficient learning compared to adults for predictive saccades (adults = 48%, children = 34%, p = 0.05). In adults brain activation was found in the frontal and occipital regions in the PRED, in the intraparietal sulcus in pPRED and in the frontal eye field, posterior intraparietal sulcus and medial regions in the tPRED task. Group-task interaction was found in the supplementary eye field and visual cortex in the PRED task, and the frontal cortex including the right frontal eye field and left frontal pole, in the pPRED condition. These results indicate that, the basic visuomotor circuitry is present in both adults and children, but fine-tuning of the activation according to the task temporal and spatial demand mature late in child development.

Altered intrinsic functional connectivity of the primary visual cortex in youth patients with comitant exotropia: a resting state fMRI study

AIM

To evaluate the differences in the functional connectivity (FC) of the primary visual cortex (V1) between the youth comitant exotropia (CE) patients and health subjects using resting functional magnetic resonance imaging (fMRI) data.

METHODS

Totally, 32 CEs (25 males and 7 females) and 32 healthy control subjects (HCs) (25 males and 7 females) were enrolled in the study and underwent the MRI scanning. Two-sample t-test was used to examine differences in FC maps between the CE patients and HCs.

RESULTS

The CE patients showed significantly less FC between the left brodmann area (BA17) and left lingual gyrus/cerebellum posterior lobe, right middle occipital gyrus, left precentral gyrus/postcentral gyrus and right inferior parietal lobule/postcentral gyrus. Meanwhile, CE patients showed significantly less FC between right BA17 and right middle occipital gyrus (BA19, 37).

CONCLUSION

Our findings show that CE involves abnormal FC in primary visual cortex in many regions, which may underlie the pathologic mechanism of impaired fusion and stereoscopic vision in CEs.

Combining two model systems of psychosis: The effects of schizotypy and sleep deprivation on oculomotor control and psychotomimetic states

Model systems of psychosis, such as schizotypy or sleep deprivation, are valuable in informing our understanding of the etiology of the disorder and aiding the development of new treatments. Schizophrenia patients, high schizotypes, and sleep-deprived subjects are known to share deficits in oculomotor biomarkers. Here, we aimed to further validate the schizotypy and sleep deprivation models and investigated, for the first time, their interactive effects on smooth pursuit eye movements (SPEM), prosaccades, antisaccades, predictive saccades, and measures of psychotomimetic states, anxiety, depression, and stress. To do so, n = 19 controls and n = 17 high positive schizotypes were examined after both a normal sleep night and 24 h of sleep deprivation. Schizotypes displayed higher SPEM global position error, catch-up saccade amplitude, and increased psychotomimetic states. Sleep deprivation impaired SPEM, prosaccade, antisaccade, and predictive saccade performance and increased levels of psychotomimetic experiences. Additionally, sleep deprivation reduced SPEM gain in schizotypes but not controls. We conclude that oculomotor impairments are observed in relation to schizotypy and following sleep deprivation, supporting their utility as biomarkers in model systems of psychosis. The combination of these models with oculomotor biomarkers may be particularly fruitful in assisting the development of new antipsychotic or pro-cognitive drugs.

A meta-analysis of functional magnetic resonance imaging studies of eye movements and visual word reading

INTRODUCTION

The pattern of eye movements during reading is substantially correlated with linguistic factors. While there have been a large number of studies on the neural mechanisms of eye movements and word reading separately, a limited number of studies have compared the activation patterns of these two processes and discussed the associations of their corresponding brain regions within the framework of naturalistic reading.

METHODS

This study conducted a meta-analysis of the existing functional magnetic resonance imaging literature on prosaccades and visual word reading using the activation likelihood estimation algorithm.

RESULTS

Our main finding was that, although prosaccades and word reading mainly activated dorsal and ventral brain areas, respectively, they both activated the left precentral gyrus (PreCG), left superior parietal lobe, right PreCG, right lingual gyrus, and bilateral medial frontal gyrus.

CONCLUSION

These findings provide new insights into cognitive processes involved with naturalistic reading, which requires both eye movements and word reading.

Differences in Saccadic Latency and Express Saccades between Skilled and Novice Ball Players in Tracking Predictable and Unpredictable Targets at Two Visual Angles

The purpose of the study was to investigate saccadic latency and percentage of express saccades involved in predictable tasks between skilled and novice ball players. Participants performed four different tasks, including time and direction unpredictable task, time predictable task, direction predictable task, and time and direction predictable task at the visual angles of 10 and 20°. Skilled ball players had shorter mean saccadic latency than novice players on direction and time and direction predictable tasks. The percentage of express saccades of skilled ball players was higher than that of novice players on the latter. Saccadic latency was shorter in the 10° condition in time and direction unpredictable task and time predictable task than for 20°. These results suggested that predictive ability might be one of the general characters distinguishing skilled ball athletes from novices in visuomotor performance. The prediction might reduce the mean difference in the saccadic latency at various visual angles.

Antisaccade-related brain activation in children with attention-deficit/hyperactivity disorder--A pilot study

While antisaccade paradigms invoke circuitry associated with cognitive control and attention-deficit/hyperactivity disorder (ADHD), there is a dearth of functional magnetic resonance imaging (fMRI) investigations using antisaccade tasks among children with ADHD. Neural correlates associated with antisaccade performance were examined with fMRI in 11 children with ADHD (10 medicated) matched to 11 typically developing children. Significantly greater brain activation in regions in right dorsolateral prefrontal cortex and caudate nucleus was observed in children with ADHD relative to the control group. This pattern separated the children into their respective groups in a taxonomic manner. Sensitivity analyses probing comorbidity and medication-specific effects showed that results were consistent; however, the caudate nucleus difference was only detectable in the full sample, or in subsets with a more relaxed cluster threshold. Antisaccade performance did not significantly differ between the groups, perhaps as a result of greater brain activation or medication effects in the ADHD group. Thus, antisaccade paradigms may have sensitivity and specificity for the investigation of cognitive control deficits and associated neural correlates in ADHD, and may contribute towards the development of new treatment approaches for children with the disorder.

The neural network of saccadic foreknowledge

Foreknowledge about upcoming events may be exploited to optimize behavioural responses. In a previous work, using an eye movement paradigm, we showed that different types of partial foreknowledge have different effects on saccadic efficiency. In the current study, we investigated the neural circuitry involved in processing of partial foreknowledge using functional magnetic resonance imaging. Fourteen subjects performed a mixed antisaccade, prosaccade paradigm with blocks of no foreknowledge, complete foreknowledge or partial foreknowledge about stimulus location, response direction or task. We found that saccadic foreknowledge is processed primarily within the well-known oculomotor network for saccades and antisaccades. Moreover, we found a consistent decrease in BOLD activity in the primary and secondary visual cortex in all foreknowledge conditions compared to the no-foreknowledge conditions. Furthermore we found that the different types of partial foreknowledge are processed in distinct brain areas: response foreknowledge is processed in the frontal eye field, while stimulus foreknowledge is processed in the frontal and parietal eye field. Task foreknowledge, however, revealed no positive BOLD correlate. Our results show different patterns of engagement in the saccade-related neural network depending upon precisely what type of information is known ahead.

Test-retest reliability of fMRI activation generated by different saccade tasks

PURPOSE

To assess the reproducibility of brain-activation and eye-movement patterns in a saccade paradigm when comparing subjects, tasks, and magnetic resonance (MR) systems.

MATERIALS AND METHODS

Forty-five healthy adults at two different sites (n = 45) performed saccade tasks with varying levels of target predictability: predictable (PRED), position predictable (pPRED), time predictable (tPRED), and prosaccade (SAC). Eye-movement pattern was tested with a repeated-measures analysis of variance. Activation maps reproducibility were estimated with the cluster overlap Jaccard index and signal variance coefficient of determination for within-subjects test-retest data, and for between-subjects data from the same and different sites.

RESULTS

In all groups latencies increased with decreasing target predictability: PRED < pPRED < tPRED < SAC (P < 0,001). Activation overlap was good to fair (>0.40) in all tasks in the within-subjects test-retest comparisons and poor (<0.40) in the tPRED for different subjects. The overlap of the different tasks for within-groups data was higher (0.40-0.68) than for the between-groups data (0.30-0.50). Activation consistency was 60-85% in the same subjects, 50-79% in different subjects, and 50-80% in different sites. In SAC, the activation found in the same and in different subjects was more consistent than in other tasks (50-80%).

CONCLUSION

The predictive saccade tasks produced evidence for brain-activation and eye-movement reproducibility.

Neural activity in the macaque putamen associated with saccades and behavioral outcome

It is now widely accepted that the basal ganglia nuclei form segregated, parallel loops with neocortical areas. The prevalent view is that the putamen is part of the motor loop, which receives inputs from sensorimotor areas, whereas the caudate, which receives inputs from frontal cortical eye fields and projects via the substantia nigra pars reticulata to the superior colliculus, belongs to the oculomotor loop. Tracer studies in monkeys and functional neuroimaging studies in human subjects, however, also suggest a potential role for the putamen in oculomotor control. To investigate the role of the putamen in saccadic eye movements, we recorded single neuron activity in the caudal putamen of two rhesus monkeys while they alternated between short blocks of pro- and anti-saccades. In each trial, the instruction cue was provided after the onset of the peripheral stimulus, thus the monkeys could either generate an immediate response to the stimulus based on the internal representation of the rule from the previous trial, or alternatively, could await the visual rule-instruction cue to guide their saccadic response. We found that a subset of putamen neurons showed saccade-related activity, that the preparatory mode (internally- versus externally-cued) influenced the expression of task-selectivity in roughly one third of the task-modulated neurons, and further that a large proportion of neurons encoded the outcome of the saccade. These results suggest that the caudal putamen may be part of the neural network for goal-directed saccades, wherein the monitoring of saccadic eye movements, context and performance feedback may be processed together to ensure optimal behavioural performance and outcomes are achieved during ongoing behaviour.

Effects of methylphenidate on basic and higher-order oculomotor functions

Eye movements are sensitive indicators of pharmacological effects on sensorimotor and cognitive processing. Methylphenidate (MPH) is one of the most prescribed medications in psychiatry. It is increasingly used as a cognitive enhancer by healthy individuals. However, little is known of its effect on healthy cognition. Here we used oculomotor tests to evaluate the effects of MPH on basic oculomotor and executive functions. Twenty-nine males were given 20mg of MPH orally in a double-blind placebo-controlled crossover design. Participants performed visually-guided saccades, sinusoidal smooth pursuit, predictive saccades and antisaccades one hour post-capsule administration. Heart rate and blood pressure were assessed prior to capsule administration, and again before and after task performance. Visually-guided saccade latency decreased with MPH (p<0.004). Smooth pursuit gain increased on MPH (p<0.001) and number of saccades during pursuit decreased (p<0.001). Proportion of predictive saccades increased on MPH (p<0.004), specifically in conditions with predictable timing. Peak velocity of predictive saccades increased with MPH (p<0.01). Antisaccade errors and latency were unaffected. Physiological variables were also unaffected. The effects on visually-guided saccade latency and peak velocity are consistent with MPH effects on dopamine in basal ganglia. The improvements in predictive saccade conditions and smooth pursuit suggest effects on timing functions.

Predictive saccade in the absence of smooth pursuit: interception of moving targets in the archer fish

Interception of fast-moving targets is a demanding task many animals solve. To handle it successfully, mammals employ both saccadic and smooth pursuit eye movements in order to confine the target to their area centralis. But how can non-mammalian vertebrates, which lack smooth pursuit, intercept moving targets? We studied this question by exploring eye movement strategies employed by archer fish, an animal that possesses an area centralis, lacks smooth pursuit eye movements, but can intercept moving targets by shooting jets of water at them. We tracked the gaze direction of fish during interception of moving targets and found that they employ saccadic eye movements based on prediction of target position when it is hit. The fish fixates on the target's initial position for ∼0.2 s from the onset of its motion, a time period used to predict whether a shot can be made before the projection of the target exits the area centralis. If the prediction indicates otherwise, the fish performs a saccade that overshoots the center of gaze beyond the present target projection on the retina, such that after the saccade the moving target remains inside the area centralis long enough to prepare and perform a shot. These results add to the growing body of knowledge on biological target tracking and may shed light on the mechanism underlying this behavior in other animals with no neural system for the generation of smooth pursuit eye movements.

Probing basal ganglia functions by saccade eye movements

The basal ganglia (BG) are a group of subcortical structures involved in diverse functions, such as motor, cognition and emotion. However, the BG do not control these functions directly, but rather modulate functional processes occurring in structures outside the BG. The BG form multiple functional loops, each of which controls different functions with similar architectures. Accordingly, to understand the modulatory role of the BG, it is strategic to uncover the mechanisms of signal processing within specific functional loops that control simple neural circuits outside the BG, and then extend the knowledge to other BG loops. The saccade control system is one of the best-understood neural circuits in the brain. Furthermore, sophisticated saccade paradigms have been used extensively in clinical research in patients with BG disorders as well as in basic research in behaving monkeys. In this review, we describe recent advances of BG research from the viewpoint of saccade control. Specifically, we account for experimental results from neuroimaging and clinical studies in humans based on the updated knowledge of BG functions derived from neurophysiological experiments in behaving monkeys by taking advantage of homologies in saccade behavior. It has become clear that the traditional BG network model for saccade control is too limited to account for recent evidence emerging from the roles of subcortical nuclei not incorporated in the model. Here, we extend the traditional model and propose a new hypothetical framework to facilitate clinical and basic BG research and dialogue in the future.

Exploring the fundamental dynamics of error-based motor learning using a stationary predictive-saccade task

The maintenance of movement accuracy uses prior performance errors to correct future motor plans; this motor-learning process ensures that movements remain quick and accurate. The control of predictive saccades, in which anticipatory movements are made to future targets before visual stimulus information becomes available, serves as an ideal paradigm to analyze how the motor system utilizes prior errors to drive movements to a desired goal. Predictive saccades constitute a stationary process (the mean and to a rough approximation the variability of the data do not vary over time, unlike a typical motor adaptation paradigm). This enables us to study inter-trial correlations, both on a trial-by-trial basis and across long blocks of trials. Saccade errors are found to be corrected on a trial-by-trial basis in a direction-specific manner (the next saccade made in the same direction will reflect a correction for errors made on the current saccade). Additionally, there is evidence for a second, modulating process that exhibits long memory. That is, performance information, as measured via inter-trial correlations, is strongly retained across a large number of saccades (about 100 trials). Together, this evidence indicates that the dynamics of motor learning exhibit complexities that must be carefully considered, as they cannot be fully described with current state-space (ARMA) modeling efforts.

Neural correlates of inter- and intra-individual saccadic reaction time differences in the gap/overlap paradigm

To examine the neural correlates of contextually differing control mechanisms in saccade initiation, we studied 18 subjects who performed two saccade paradigms in a pseudo-random order, while their eye movements were recorded in the MRI scanner (1.5 T). In the gap task the fixation point was extinguished 200 ms before target onset, and in the overlap task the fixation point vanished 500 ms after target onset. Subjects were asked to maintain stable fixation in the fixation period and to quickly saccade to peripherally presented targets. Inter-individual activation differences were assessed using regression analyses at the second level, with mean saccadic reaction time (SRT) of subjects as a covariate. To identify brain regions varying with trial-by-trial changes in SRTs, we included SRTs as a parametric modulation regressor in the general linear model. All analyses were regions of interest based and were performed separately for the gap and overlap conditions. For the gap paradigm, we did not obtain activation in regions previously shown to be involved in preparatory processes with much longer gap periods. Interestingly, both inter- and intra-individual variability analyses revealed a positive correlation of activation in frontal and parietal eye-movement regions with SRTs, indicating that slower saccade performance is possibly associated with higher cortical control. For the overlap paradigm, the trial-by-trial variability analysis revealed a positive correlation of activation in the right opercular inferior frontal gyrus with SRTs, possibly linked to fixation-related processes that have to be overcome to perform a speeded saccade in presence of a fixation point.

Deficit of inhibition motor control in untreated patients with schizophrenia: further support from visually guided saccade paradigms

In addition to classical delusional, negative, and cognitive deficit, schizophrenia has consistently been associated with impairments in saccadic eye movements, e.g., an increased error rate in the antisaccade task. We hypothesized that a deficit in inhibitory control is a core defect in untreated patients with schizophrenia leading to impairment in different oculomotor paradigms. Ten drug-free or drug-naïve patients with schizophrenia were matched in age and gender to 11 healthy controls with no psychoactive substance use or abuse. They were explored using reflexive saccades with unpredictable targets with or without the gap procedure, predictive saccades and a fixation/distracter paradigm. Patients with schizophrenia displayed shorter latency in reflexive and predictive saccades. In the GAP condition, patients made more anticipatory saccades, fewer regular saccades, and had a shorter latency of express saccades than controls. In addition, patients had an increased error rate in the fixation/distracters task. Altogether, these results provide new evidence of reduced prefrontal inhibitory regulation of subcortical and brainstem systems involved in the control of saccades.

Effect of D-amphetamine on inhibition and motor planning as a function of baseline performance

RATIONALE

Baseline performance has been reported to predict dopamine (DA) effects on working memory, following an inverted-U pattern. This pattern may hold true for other executive functions that are DA-sensitive.

OBJECTIVES

The objective of this study is to investigate the effect of D: -amphetamine, an indirect DA agonist, on two other putatively DA-sensitive executive functions, inhibition and motor planning, as a function of baseline performance.

METHODS

Participants with no prior stimulant exposure participated in a double-blind crossover study of a single dose of 0.3 mg/kg, p.o. of D: -amphetamine and placebo. Participants were divided into high and low groups, based on their performance on the antisaccade and predictive saccade tasks on the baseline day. Executive functions, mood states, heart rate and blood pressure were assessed before (T0) and after drug administration, at 1.5 (T1), 2.5 (T2) and 3.5 h (T3) post-drug.

RESULTS

Antisaccade errors decreased with D: -amphetamine irrespective of baseline performance (p = 0.025). For antisaccade latency, participants who generated short-latency antisaccades at baseline had longer latencies on D: -amphetamine than placebo, while those with long-latency antisaccades at baseline had shorter latencies on D: -amphetamine than placebo (drug x group, p = 0.04). D: -amphetamine did not affect motor planning. Ratings of mood improved on D: -amphetamine (p < 0.001). Magnitude of D: -amphetamine-induced changes in elation was related to baseline reaction time variability.

CONCLUSIONS

D: -amphetamine reduced antisaccade error rates in healthy controls, replicating and extending findings with DA agonists in clinical populations. D: -amphetamine had baseline-dependent effects on antisaccade latency, consistent with an inverted-U relationship between performance and DA activity.

High-field FMRI reveals brain activation patterns underlying saccade execution in the human superior colliculus

Background

The superior colliculus (SC) has been shown to play a crucial role in the initiation and coordination of eye- and head-movements. The knowledge about the function of this structure is mainly based on single-unit recordings in animals with relatively few neuroimaging studies investigating eye-movement related brain activity in humans.

Methodology/Principal Findings

The present study employed high-field (7 Tesla) functional magnetic resonance imaging (fMRI) to investigate SC responses during endogenously cued saccades in humans. In response to centrally presented instructional cues, subjects either performed saccades away from (centrifugal) or towards (centripetal) the center of straight gaze or maintained fixation at the center position. Compared to central fixation, the execution of saccades elicited hemodynamic activity within a network of cortical and subcortical areas that included the SC, lateral geniculate nucleus (LGN), occipital cortex, striatum, and the pulvinar.

Conclusions/Significance

Activity in the SC was enhanced contralateral to the direction of the saccade (i.e., greater activity in the right as compared to left SC during leftward saccades and vice versa) during both centrifugal and centripetal saccades, thereby demonstrating that the contralateral predominance for saccade execution that has been shown to exist in animals is also present in the human SC. In addition, centrifugal saccades elicited greater activity in the SC than did centripetal saccades, while also being accompanied by an enhanced deactivation within the prefrontal default-mode network. This pattern of brain activity might reflect the reduced processing effort required to move the eyes toward as compared to away from the center of straight gaze, a position that might serve as a spatial baseline in which the retinotopic and craniotopic reference frames are aligned.

Eye tracking dysfunction in schizophrenia: characterization and pathophysiology

Eye tracking dysfunction (ETD) is one of the most widely replicated behavioral deficits in schizophrenia and is over-represented in clinically unaffected first-degree relatives of schizophrenia patients. Here, we provide an overview of research relevant to the characterization and pathophysiology of this impairment. Deficits are most robust in the maintenance phase of pursuit, particularly during the tracking of predictable target movement. Impairments are also found in pursuit initiation and correlate with performance on tests of motion processing, implicating early sensory processing of motion signals. Taken together, the evidence suggests that ETD involves higher-order structures, including the frontal eye fields, which adjust the gain of the pursuit response to visual and anticipated target movement, as well as early parts of the pursuit pathway, including motion areas (the middle temporal area and the adjacent medial superior temporal area). Broader application of localizing behavioral paradigms in patient and family studies would be advantageous for refining the eye tracking phenotype for genetic studies.

Correlates between neurological soft signs and saccadic parameters in schizophrenia

OBJECTIVE

Neurological Soft Signs (NSS) and impairments in oculomotor saccadic paradigms are both frequent in patients with schizophrenia but their correlation has never been explored.

METHODS

78 patients with DSM-IV schizophrenia (including 43 non-treated) and 41 matched healthy controls were tested for NSS, and on three saccadic tasks: prosaccades, predictive saccades and memory-guided saccades) using infrared oculometry. We analyzed correlations between NSS scores and latencies in all three tasks, rate of errors in memory-guided saccades, and rate of anticipated predictive saccades.

RESULTS

No correlations were found in healthy controls. In the patient group, the NSS total and motor coordination scores were positively correlated with three saccadic variables: the latency of prosaccades (r=0.36, p<0.01 and r=0.36, p<0.01 respectively), of memory-guided saccades (r=0.35, p<0.01 and r=0.32, p<0.05 respectively) and, negative correlations were found, with the rate of anticipated predictive saccades (r=-0.33, p<0.01; r=-0.35, p<0.01 respectively). NSS total, motor coordination and sensory integration scores were correlated to the latency of non-anticipated predictive saccades (r=0.34, p<0.01; r=0.24, p<0.05 and r=0.40, p<0.001 respectively). The NSS total, motor integration and sensory integration scores were correlated with the rate of errors in memory-guided saccades (r=0.38, p<0.01; r=0.37, p<0.01 and r=0.34, p<0.01 respectively).

CONCLUSIONS

These results support a common pathological mechanism with partial overlapping neural substrates between NSS and saccades in schizophrenia.

Neurophysiology and neuroanatomy of reflexive and volitional saccades: evidence from studies of humans

This review provides a summary of the contributions made by human functional neuroimaging studies to the understanding of neural correlates of saccadic control. The generation of simple visually guided saccades (redirections of gaze to a visual stimulus or pro-saccades) and more complex volitional saccades require similar basic neural circuitry with additional neural regions supporting requisite higher level processes. The saccadic system has been studied extensively in non-human (e.g., single-unit recordings) and human (e.g., lesions and neuroimaging) primates. Considerable knowledge of this system's functional neuroanatomy makes it useful for investigating models of cognitive control. The network involved in pro-saccade generation (by definition largely exogenously-driven) includes subcortical (striatum, thalamus, superior colliculus, and cerebellar vermis) and cortical (primary visual, extrastriate, and parietal cortices, and frontal and supplementary eye fields) structures. Activation in these regions is also observed during endogenously-driven voluntary saccades (e.g., anti-saccades, ocular motor delayed response or memory saccades, predictive tracking tasks and anticipatory saccades, and saccade sequencing), all of which require complex cognitive processes like inhibition and working memory. These additional requirements are supported by changes in neural activity in basic saccade circuitry and by recruitment of additional neural regions (such as prefrontal and anterior cingulate cortices). Activity in visual cortex is modulated as a function of task demands and may predict the type of saccade to be generated, perhaps via top-down control mechanisms. Neuroimaging studies suggest two foci of activation within FEF - medial and lateral - which may correspond to volitional and reflexive demands, respectively. Future research on saccade control could usefully (i) delineate important anatomical subdivisions that underlie functional differences, (ii) evaluate functional connectivity of anatomical regions supporting saccade generation using methods such as ICA and structural equation modeling, (iii) investigate how context affects behavior and brain activity, and (iv) use multi-modal neuroimaging to maximize spatial and temporal resolution.

Human brain activity time-locked to rapid eye movements during REM sleep

To identify the neural substrate of rapid eye movements (REMs) during REM sleep in humans, we conducted simultaneous functional magnetic resonance imaging (fMRI) and polysomnographic recording during REM sleep. Event-related fMRI analysis time-locked to the occurrence of REMs revealed that the pontine tegmentum, ventroposterior thalamus, primary visual cortex, putamen and limbic areas (the anterior cingulate, parahippocampal gyrus and amygdala) were activated in association with REMs. A control experiment during which subjects made self-paced saccades in total darkness showed no activation in the visual cortex. The REM-related activation of the primary visual cortex without visual input from the retina provides neural evidence for the existence of human ponto-geniculo-occipital waves (PGO waves) and a link between REMs and dreaming. Furthermore, the time-course analysis of blood oxygenation level-dependent responses indicated that the activation of the pontine tegmentum, ventroposterior thalamus and primary visual cortex started before the occurrence of REMs. On the other hand, the activation of the putamen and limbic areas accompanied REMs. The activation of the parahippocampal gyrus and amygdala simultaneously with REMs suggests that REMs and/or their generating mechanism are not merely an epiphenomenon of PGO waves, but may be linked to the triggering activation of these areas.

Distributed representations of the "preparatory set" in the frontal oculomotor system: a TMS study

Background

The generation of saccades is influenced by the level of "preparatory set activity" in cortical oculomotor areas. This preparatory activity can be examined using the gap-paradigm in which a temporal gap is introduced between the disappearance of a central fixation target and the appearance of an eccentric target.

Methods

Ten healthy subjects made horizontal pro- or antisaccades in response to lateralized cues after a gap period of 200 ms. Single-pulse transcranial magnetic stimulation (TMS) was applied to the dorsolateral prefrontal cortex (DLPFC), frontal eye field (FEF), or supplementary eye field (SEF) of the right hemisphere 100 or 200 ms after the disappearance of the fixation point. Saccade latencies were measured to probe the disruptive effect of TMS on saccade preparation. In six individuals, we gave realistic sham TMS during the gap period to mimic auditory and somatosensory stimulation without stimulating the cortex.

Results

TMS to DLPFC, FEF, or SEF increased the latencies of contraversive pro- and antisaccades. This TMS-induced delay of saccade initiation was particularly evident in conditions with a relatively high level of preparatory set activity: The increase in saccade latency was more pronounced at the end of the gap period and when participants prepared for prosaccades rather than antisaccades. Although the "lesion effect" of TMS was stronger with prefrontal TMS, TMS to FEF or SEF also interfered with the initiation of saccades. The delay in saccade onset induced by real TMS was not caused by non-specific effects because sham stimulation shortened the latencies of contra- and ipsiversive anti-saccades, presumably due to intersensory facilitation.

Conclusion

Our results are compatible with the view that the "preparatory set" for contraversive saccades is represented in a distributed cortical network, including the contralateral DLPFC, FEF and SEF.

Predictive eye and hand movements are differentially affected by schizophrenia

BACKGROUND

Schizophrenic patients are known to have problems suppressing reflexive eye movements. This is considered to indicate a dysfunction in prefrontal cortex. As the eye and hand motor systems are tightly coupled, we investigated whether predictive hand movements and eye-hand coordination are unimpaired in schizophrenic patients.

METHODS

Saccades and hand movements of 19 patients during an acute schizophrenic episode and 19 controls were measured in a task in which the predictability of target timing was varied.

RESULTS

Schizophrenic patients generated more anticipatory and less visually triggered saccades than controls with both non-predictable and predictable target timing. Anticipatory saccades in the wrong direction were clearly directed towards previous target positions, indicating that they are indicators of erroneous prediction rather than of fixation instability. In contrast to saccades, the number of anticipatory and visually triggered hand movements was the same in patients as in controls. As a consequence, patients took longer to initiate a hand movement after a saccade than controls.

CONCLUSIONS

Schizophrenic patients show increased predictive saccadic activity, but no qualitative changes in predictive saccades. Since prediction itself was not disturbed, the patients' deficit rather lies in the suppression or gating of anticipatory saccades than in their generation. This may be explained by a selective dysfunction of the basal ganglia oculomotor loop. As predictive hand movements were unimpaired, the problems in eye-hand coordination as expressed by a longer initiation time of hand movements relative to saccades are a direct consequence of impaired predictive saccadic behaviour.

Distinct causal influences of parietal versus frontal areas on human visual cortex: evidence from concurrent TMS-fMRI

It has often been proposed that regions of the human parietal and/or frontal lobe may modulate activity in visual cortex, for example, during selective attention or saccade preparation. However, direct evidence for such causal claims is largely missing in human studies, and it remains unclear to what degree the putative roles of parietal and frontal regions in modulating visual cortex may differ. Here we used transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) concurrently, to show that stimulating right human intraparietal sulcus (IPS, at a site previously implicated in attention) elicits a pattern of activity changes in visual cortex that strongly depends on current visual context. Increased intensity of IPS TMS affected the blood oxygen level-dependent (BOLD) signal in V5/MT+ only when moving stimuli were present to drive this visual region, whereas TMS-elicited BOLD signal changes were observed in areas V1-V4 only during the absence of visual input. These influences of IPS TMS upon remote visual cortex differed significantly from corresponding effects of frontal (eye field) TMS, in terms of how they related to current visual input and their spatial topography for retinotopic areas V1-V4. Our results show directly that parietal and frontal regions can indeed have distinct patterns of causal influence upon functional activity in human visual cortex.

fMRI studies of eye movement control: investigating the interaction of cognitive and sensorimotor brain systems

Functional neuroimaging studies of eye movement control have been a useful approach for investigating the interaction of cognitive and sensorimotor brain systems. Building on unit recording studies of behaving nonhuman primates and clinical studies of patients with a focal brain lesion, functional neuroimaging studies have elucidated a pattern of hierarchical organization through which prefrontal and premotor systems interact with sensorimotor systems to support context-dependent adaptive behavior. Studies of antisaccades, memory-guided saccades, and predictive saccades have helped clarify how cognitive brain systems support contextually guided and internally generated action. The use of cognitive and sensorimotor eye movement paradigms is being used to develop a better understanding of life span changes in neurocognitive systems from childhood to late life, and about behavioral and systems-level brain abnormalities in neuropsychiatric disorders.

The contribution of the human FEF and SEF to smooth pursuit initiation

Smooth pursuit eye movements function to keep moving targets foveated. Behavioral studies have shown that pursuit is particularly effective for predictable target motion. There is evidence that both the frontal eye field (FEF) and supplementary eye field (SEF) (also known as the dorsomedial frontal cortex) contribute to pursuit control. The goal of the current experiment was to determine whether these 2 areas made different contributions to the initiation of pursuit in response to predictable compared with unpredictable target motion. Transcranial magnetic stimulation (TMS) was used in 5 healthy human participants to temporarily disrupt each area around the time of target motion onset. TMS over the FEF delayed contraversive pursuit markedly more than ipsiversive pursuit and this direction-dependent difference was more deeply modulated during pursuit of unpredictable than predictable target motion. By contrast, TMS over the SEF resulted in a much more muted modulation of pursuit latency that was similar across both predictable and unpredictable conditions. Taken together, we conclude that the human FEF, but not the SEF, makes a significant contribution to the processing required during the preparation of contraversive pursuit responses to unpredictable target motion and this contribution is less vital during pursuit to predictable target motion.

An internal clock generates repetitive predictive saccades

Previously we demonstrated the presence of a behavioral phase transition between reactive and predictive eye tracking of alternating targets. Prior studies of repetitive movements have proposed that an "internal clock" is the neural mechanism by which interval timing is achieved. In the present report we tested whether predictive oculomotor (saccade) tracking is based on an internal time reference (clock) by examining the effect of transient perturbations to the periodic pacing stimulus. These perturbations consisted of altering the timing of the stimulus (abruptly increasing or decreasing the inter-stimulus interval) or extinguishing the targets altogether. Although reactive tracking (at low pacing rates) was greatly affected by these timing perturbations, once predictive tracking was established subjects continued to time their eye movement responses at the pre-existing rate despite the perturbation. As expected from certain clock models, inter-stimulus intervals for predictive tracking followed Weber's law and the scalar property (timing variability increases in proportion to interval duration), but this was not true for reactive tracking. In addition, the perturbation results show that subjects can establish an internal representation of target pacing (the internal clock) in as little as two eye-movement intervals, which suggests that this mechanism is relevant for real-world situations. These findings are consistent with the presence of an internal clock for the generation of these predictive movements, and demonstrate that the neural mechanism responsible for this behavior is temporally accurate and flexible.

Basal ganglia-thalamocortical circuitry disruptions in schizophrenia during delayed response tasks

BACKGROUND

Schizophrenia is characterized by executive functioning deficits, presumably mediated by prefrontal cortex dysfunction. For example, schizophrenia participants show performance deficits on ocular motor delayed response (ODR) tasks, which require both inhibition and spatial working memory for correct performance.

METHODS

The present functional magnetic resonance imaging (fMRI) study compared neural activity of 14 schizophrenia and 14 normal participants while they performed ODR tasks.

RESULTS

Schizophrenia participants generated: 1) more trials with anticipatory saccades (saccades made during the delay period), 2) memory saccades with longer latencies, and 3) memory saccades of decreased accuracy. Increased blood oxygenation level-dependent (BOLD) signal changes were observed in both groups in ocular motor circuitry (e.g., supplementary eye fields [SEF], lateral frontal eye fields [FEF], inferior parietal lobule [IPL], cuneus, and precuneus). The normal, but not the schizophrenia, group demonstrated BOLD signal changes in dorsolateral prefrontal regions (right Brodmann area [BA] 9 and bilateral BA 10), medial FEF, insula, thalamus, and basal ganglia. Correlations between percentage of anticipatory saccade trials and BOLD signal changes were more similar between groups for subcortical regions and less similar for cortical regions.

CONCLUSIONS

These results suggest that executive functioning deficits in schizophrenia may be associated with dysfunction of the basal ganglia-thalamocortical circuitry, evidenced by decreased prefrontal cortex, basal ganglia, and thalamus activity in the schizophrenia group during ODR task performance.

Self-paced saccades and saccades to oddball targets in Parkinson's disease

Patients with Parkinson's disease (PD) manifest difficulty in initiation and execution of movements, particularly when movements are sequential, simultaneous or repetitive. Eye movements are particularly effective in evaluating motor impairments. We utilized a series of saccadic eye movement paradigms to explore the ability of 13 patients with mild-moderate PD and 13 age-matched healthy controls to self-pace saccades between two continuously illuminated targets, before and after an externally cued tracking period, and respond to unexpected changes in task demand. The latter was explored by measuring saccadic responses to unexpected "oddball" targets that appeared during a well-learned reciprocating sequence of saccades, in either the opposite direction to that expected or at twice the anticipated extent. Results indicated that all participants demonstrated a marked increase in saccade amplitudes from the externally cued saccade tracking to the self-paced saccades. Unexpectedly, this difference was magnified in PD patients. Self-paced saccades before externally cueing were also more frequent than requested in the PD group, but timing improved following external cueing. The second key finding was that while patients were able to respond to unexpected changes in target amplitude, performance was more variable (in terms of latency and accuracy) when responding to unexpected changes in target direction. Hence, beneficial effects of external cueing on the timing of self-paced saccades may be mediated through cortical regions, placing less emphasis on striatal regions known to be compromised in PD. Additionally, responding to changes in saccade direction (but not amplitude) may rely on basal ganglia circuitry.

Direction-dependent visual cortex activation during horizontal optokinetic stimulation (fMRI study)

Looking at a moving pattern induces optokinetic nystagmus (OKN) and activates an assembly of cortical areas in the visual cortex, including lateral occipitotemporal (motion-sensitive area MT/V5) and adjacent occipitoparietal areas as well as ocular motor areas such as the prefrontal cortex, frontal, supplementary, and parietal eye fields. The aim of this functional MRI (fMRI) study was to investigate (1) whether stimulus direction-dependent effects can be found, especially in the cortical eye fields, and (2) whether there is a hemispheric dominance of ocular motor areas. In a group of 15 healthy subjects, OKN in rightward and leftward directions was visually elicited and statistically compared with the control condition (stationary target) and with each other. Direction-dependent differences were not found in the cortical eye fields, but an asymmetry of activation occurred in paramedian visual cortex areas, and there were stronger activations in the hemisphere contralateral to the slow OKN phase (pursuit). This can be explained by a shift of the mean eye position of gaze (beating field) in the direction of the fast nystagmus phases of approximately 2.6 degrees, causing asymmetrical visual cortex stimulation. The absence of a significant difference in the activation pattern of the cortical eye fields supports the view that the processing of eye movements in both horizontal directions is mediated in the same cortical ocular motor areas. Furthermore, no hemispheric dominance for OKN processing was found in right-handed volunteers.

Improving antisaccade performance in adolescents with attention-deficit/hyperactivity disorder (ADHD)

The goal of the study was to examine the effects of task manipulations on antisaccade accuracy and response times (RTs) of adolescents with attention-deficit/hyperactivity disorder (ADHD), age-matched controls, 10-year-olds and young adults. Order effects were tested by administering the task at the beginning and end of the session. Other manipulations involved a visual landmark to reduce demands on working memory and internal generation of saccades; spatially specific and non-specific cues at three intervals; and central engagement of attention through perceptual and cognitive means at three intervals. As expected, adolescents with ADHD were impaired relative to age-matched controls in terms of accuracy and saccadic RT on the first administration of the task. Although their accuracy improved with most of the manipulations, it did not improve disproportionately compared to age-matched controls. Nevertheless, with most of the manipulations, they could achieve the same level of accuracy as unaided controls on the first administration of the task. In contrast, the saccadic RTs of the ADHD group came close to normal under several conditions, indicating that elevated antisaccade RTs in this disorder may be related to attentional factors. The ADHD group made more premature saccades and fewer corrective saccades than both the age-matched and younger groups, suggesting difficulties with impulsivity and goal neglect. The findings suggest that cognitive scaffolds can ameliorate at least some of the inhibition deficits in adolescents with ADHD.

Local morphology predicts functional organization of the dorsal premotor region in the human brain

A confusing picture of the functional organization of the dorsal premotor region of the human brain emerged when functional neuroimaging studies that either examined visuomotor hand conditional activity or attempted to localize the human frontal eye field reported activity increases at the same general location, namely the junction of the superior precentral sulcus with the superior frontal sulcus. The present functional magnetic resonance imaging study examined visuomotor hand conditional activity and the locus of the frontal eye field as defined by a standard task, on a subject-by-subject basis, to clarify their location and reveal relationships between the pattern of local morphology and functional activity. The results demonstrate that visuomotor hand conditional activity and the frontal eye field lie within distinct parts of the superior precentral sulcus, revealing an organization of the human premotor cortex consistent with that observed in experimental studies in the monkey.

Saccades in children

Saccades are necessary for optimal vision. Little is known about saccades in children. We recorded saccades using an infrared eye tracker in 39 children, aged 8-19 years. Participants made saccades to visual targets that stepped 10 degrees or 15 degrees horizontally and 5 degrees or 10 degrees vertically at unpredictable time intervals. Saccadic latency decreased significantly with increasing age, while saccadic gain and peak velocity did not vary with age. Saccadic gains and peak velocities in children are similar to reported adult values. This implies maturity of the neural circuits responsible for making saccades accurate and fast. Saccade latency decreases as the brain matures.

The use of working memory for task prediction: What benefits accrue from different types of foreknowledge?

The assumption that the deployment of executive processes invariably improves task performance is implicit to cognitive theory. In particular, working memory can be used to retain and update historical information about predictable trial sequences (foreknowledge) so that subjects can anticipate and prepare for the upcoming trial more effectively. We review the effects of different types of foreknowledge on response accuracy and latency, particularly in relation to experiments investigating saccadic eye movements in humans. While it is possible to make all aspects of an impending trial predictable, varying the predictability of different components of the trial independently can reveal which cognitive operations are potentially modifiable by foreknowledge. These operations include stimulus processing, retrieval of task-set rules, and response preparation, among others. The available data suggest that, while response preparation can be completed and the response even executed before the stimulus appears (i.e. anticipation) when the subject possesses complete task-foreknowledge (knowing both the stimulus to appear and the response required), foreknowledge of the task-set alone does not permit advance configuration of the task-set rules. A taxonomy for foreknowledge is proposed, including foreknowledge for timing, stimulus, set, response, and task. Work on differentiating these effects in neurophysiology, neuroimaging, and neuropsychology is still in the early stages.

Saccades in children with spina bifida and Chiari type II malformation

BACKGROUND

Saccades are essential for optimal visual function. Chiari type II malformation (CII) is a congenital anomaly of the cerebellum and brainstem, associated with spina bifida.

OBJECTIVE

To investigate the effects of CII on saccades and correlate saccadic parameters with brain MRI measurements.

METHODS

Saccades were recorded in 21 participants with CII, aged 8 to 19, using an infrared eye tracker. Thirty-nine typically developing children served as controls. Participants made saccades to horizontal and vertical target steps. Nineteen participants with CII had MRI. Regression analyses were used to investigate the effects of spinal lesion level, number of shunt revisions, presence of nystagmus, and midsagittal MRI measurements on saccades.

RESULTS

Saccadic amplitude gains, asymptotic peak velocities, and latencies did not differ between the control and CII groups (p > 0.01). No significant differences were found between saccadic gains, asymptotic peak velocities or latencies, and spinal lesion level, number of shunt revisions, presence of nystagmus, or MRI measurements.

CONCLUSIONS

Saccades were normal in most participants with Chiari II malformation (CII). Neural coding of saccades is robust and is typically not affected by the anatomic deformity of CII.

Transcranial magnetic stimulation of frontal oculomotor regions during smooth pursuit

Both the frontal eye fields (FEFs) and supplementary eye fields (SEFs) are known to be involved in smooth pursuit eye movements. It has been shown recently that stimulation of the smooth-pursuit area of the FEF [frontal pursuit area (FPA)] in monkey increases the pursuit response to unexpected changes in target motion during pursuit. In the current study, we applied transcranial magnetic stimulation (TMS) to the FPA and SEF in humans during sinusoidal pursuit to assess its effects on the pursuit response to predictable, rather than unexpected, changes in target motion. For the FPA, we found that TMS applied immediately before the target reversed direction increased eye velocity in the new direction, whereas TMS applied in mid-cycle, immediately before the target began to slow, decreased eye velocity. For the SEF, TMS applied at target reversal increased eye velocity in the new direction but had no effect on eye velocity when applied at mid-cycle. TMS of the control region (leg region of the somatosensory cortex) did not affect eye velocity at either point. Previous stimulation studies of FPA during pursuit have suggested that this region is involved in controlling the gain of the transformation of visual signals into pursuit motor commands. The current results suggest that the gain of the transformation of predictive signals into motor commands is also controlled by the FPA. The effect of stimulation of the SEF is distinct from that of the FPA and suggests that its role in sinusoidal pursuit is primarily at the target direction reversal.

Evidence for the importance of basal ganglia output nuclei in semantic event sequencing: an fMRI study

Semantic event sequencing is the ability to plan ahead and order meaningful events chronologically. To investigate the neural systems supporting this ability, an fMRI picture sequencing task was developed. Participants sequenced a series of four pictures presented in random order based on the temporal relationship among them. A control object discrimination task was designed to be comparable to the sequencing task regarding semantic, visuospatial, and motor processing requirements but without sequencing demands. fMRI revealed significant activation in the dorsolateral prefrontal cortex and globus pallidus internal part in the picture sequencing task compared with the control task. The findings suggest that circuits involving the frontal lobe and basal ganglia output nuclei are important for picture sequencing and more generally for the sequential ordering of events. This is consistent with the idea that the basal ganglia output nuclei are critical not only for motor but also for high-level cognitive function, including behaviors involving meaningful information. We suggest that the interaction between the frontal lobes and basal ganglia output nuclei in semantic event sequencing can be generalized to include the sequential ordering of behaviors in which the selective updating of neural representations is the key computation.

Electroencephalography/magnetoencephalography study of cortical activities preceding prosaccades and antisaccades

The temporal and spatial characteristics of brain activity preceding prosaccades and antisaccades were investigated using source reconstructions of 64-channel electroencephalography and 148-channel magnetoencephalography data. Stimulus-locked data showed early cuneus activity was stronger during antisaccades, and later occipital gyrus activity was stronger preceding prosaccades, which suggests a top-down influence on early visual processing. Response-locked data showed that supplementary eye field, prefrontal cortex, and medial frontal eye field activity was greater for antisaccades than for prosaccades prior to saccade generation. Lateral frontal eye field activity appeared to be inhibited prior to antisaccade response generation. The spatial and temporal resolution of combined electroencephalography/magnetoencephalography data allows the evaluation of specific cortical activities preceding saccades and for demonstration of how activities differ as a function of response contingencies.