Smooth pursuit eye movements in 1,087 men: effects of schizotypy, anxiety, and depression

Differential eye movement features between Alzheimer's disease patients with and without depressive symptoms

BACKGROUND

Accurately diagnosing depressive symptoms in Alzheimer's disease (AD) patients is often challenging. Eye movement parameters have been demonstrated as biomarkers for assessing cognition and psychological conditions.

AIM

To investigate the differences in eye movement between AD patients with and without depressive symptoms.

METHODS

Eye movement data of 65 AD patients were compared between the depressed AD (D-AD) and non-depressed AD (nD-AD) groups. Logistic regression analysis was employed to identify diagnostic biomarkers and the ROC curve was plotted. The correlation between eye movement and HAMD-17 scores was assessed by partial correlation analysis.

RESULTS

The D-AD patients showed longer saccade latency and faster average/peak saccade velocities in the overlap prosaccade test, longer average reaction time and faster average saccade velocity in the gap prosaccade test, longer start-up durations, slower pursuit velocity, more offsets, and larger total offset degrees in the smooth pursuit test, and poorer fixation stability in both the central and lateral fixation tests compared to nD-AD patients. The start-up duration in the smooth pursuit test and the number of offsets in the central fixation test were identified as the diagnostic eye movement parameters for D-AD patients with the area under the ROC curves of 0.8011. Partial correlation analysis revealed that the start-up duration and pursuit velocity in the smooth pursuit test and the total offset degrees in the lateral fixation test were correlated with HAMD-17 scores in D-AD patients.

DISCUSSION AND CONCLUSIONS

Eye movement differences may help to differentiate D-AD patients from nD-AD patients in a non-invasive and cost-effective manner.

Neural Correlates of Smooth Pursuit Eye Movements in Schizotypy and Recent Onset Psychosis: A Multivariate Pattern Classification Approach

Schizotypy refers to a set of personality traits that bear resemblance, at subclinical level, to psychosis. Despite evidence of similarity at multiple levels of analysis, direct comparisons of schizotypy and clinical psychotic disorders are rare. Therefore, we used functional magnetic resonance imaging (fMRI) to examine the neural correlates and task-based functional connectivity (psychophysiological interactions; PPI) of smooth pursuit eye movements (SPEM) in patients with recent onset psychosis (ROP; n = 34), participants with high levels of negative (HNS; n = 46) or positive (HPS; n = 41) schizotypal traits, and low-schizotypy control participants (LS; n = 61) using machine-learning. Despite strong previous evidence that SPEM is a highly reliable marker of psychosis, patients and controls could not be significantly distinguished based on SPEM performance or blood oxygen level dependent (BOLD) signal during SPEM. Classification was, however, significant for the right frontal eye field (FEF) seed region in the PPI analyses but not for seed regions in other key areas of the SPEM network. Applying the right FEF classifier to the schizotypal samples yielded decision scores between the LS and ROP groups, suggesting similarities and dissimilarities of the HNS and HPS samples with the LS and ROP groups. The very small difference between groups is inconsistent with previous studies that showed significant differences between patients with ROP and controls in both SPEM performance and underlying neural mechanisms with large effect sizes. As the current study had sufficient power to detect such differences, other reasons are discussed.

Sensory gating is related to positive and disorganised schizotypy in contrast to smooth pursuit eye movements and latent inhibition

Since the characteristics and symptoms of both schizophrenia and schizotypy are manifested heterogeneously, it is possible that different endophenotypes and neurophysiological measures (sensory gating and smooth pursuit eye movement errors) represent different clusters of symptoms. Participants (N = 205) underwent a standard conditioned-pairing paradigm to establish their sensory gating ratio, a smooth-pursuit eye-movement task, a latent inhibition task, and completed the Schizotypal Personality Questionnaire. A Multidimensional Scaling analysis revealed that sensory gating was related to positive and disorganised dimensions of schizotypy. Latent inhibition and prepulse inhibition were not related to any dimension of schizotypy. Smooth pursuit eye movement error was unrelated to sensory gating and latent inhibition, but was related to negative dimensions of schizotypy. Our findings suggest that the symptom clusters associated with two main endophenotypes are largely independent. To fully understand symptomology and outcomes of schizotypal traits, the different subtypes of schizotypy (and potentially, schizophrenia) ought to be considered separately rather than together.

Replicability and reliability of the background and target velocity effects in smooth pursuit eye movements

When we follow a slowly moving target with our eyes, we perform smooth pursuit eye movements (SPEM). Previous investigations point to significantly and robustly reduced SPEM performance in the presence of a stationary background and at higher compared to lower target velocities. However, the reliability of these background and target velocity effects has not yet been investigated systematically. To address this issue, 45 healthy participants (17 m, 28 f) took part in two experimental sessions 7 days apart. In each session, participants were instructed to follow a horizontal SPEM target moving sinusoidally between ±7.89° at three different target velocities, corresponding to frequencies of 0.2, 0.4 and 0.6 Hz. Each target velocity was presented once with and once without a stationary background, resulting in six blocks. The blocks were presented twice per session in order to additionally explore potential task length effects. To assess SPEM performance, velocity gain was calculated as the ratio of eye to target velocity. In line with previous research, detrimental background and target velocity effects were replicated robustly in both sessions with large effect sizes. Good to excellent test-retest reliabilities were obtained at higher target velocities and in the presence of a stationary background, whereas lower reliabilities occurred with slower targets and in the absence of background stimuli. Target velocity and background effects resulted in largely good to excellent reliabilities. These findings not only replicated robust experimental effects of background and target velocity at group level, but also revealed that these effects can be translated into reliable individual difference measures.

Mechanisms of smooth pursuit eye movements in schizotypy

Several studies suggest that highly schizotypal individuals display a deficit in smooth pursuit eye movements (SPEM), which are considered an important biomarker of schizophrenia. In schizophrenia, abnormal SPEM is thought to be driven by impairments in motion perception. In schizotypy, the processes underlying reduced SPEM performance have not been examined so far, and there are no studies on motion perception deficits in schizotypy. Thus, in this registered report, we aimed to investigate whether motion perception is impaired in highly schizotypal individuals, and how it contributes to SPEM performance. On an exploratory basis, we were interested in the association between schizotypy and prediction, another mechanism underlying SPEM. To address this issue, participants with high total scores of the Oxford-Liverpool Inventory of Feelings and Experiences (O-LIFE short form) and control participants with low scores (N = 86 in each group) performed a standard sinusoidal SPEM task, random dot kinematograms to measure motion perception, and a blanking SPEM task to assess prediction abilities. Group comparisons as well as mediator analyses were carried out to identify whether motion perception or prediction are responsible for SPEM performance in schizotypy. We found reduced blanking SPEM performance in schizotypes compared to controls, but no group differences regarding sinusoidal SPEM and motion perception. Although no significant mediators were identified for SPEM performance in schizotypes, an exploratory analysis revealed an association between motion perception and SPEM gain in high, but not in low schizotypy. Our findings imply that despite the schizotypy-related impairment in prediction, motion perception seems to be a more important predictor of SPEM performance in schizotypes. A deficit in prediction that does not relate to SPEM performance suggests that protective factors (e.g., other cognitive processes) might operate in schizotypal individuals to maintain SPEM performance on a healthy level.

Working memory load improves diagnostic performance of smooth pursuit eye movement in mild traumatic brain injury patients with protracted recovery

Smooth pursuit eye movements have been investigated as a diagnostic tool for mild traumatic brain injury (mTBI). However, the degree to which smooth pursuit differentiates mTBI patients from healthy controls (i.e. its diagnostic performance) is only moderate. Our goal was to establish if simultaneous performance of smooth pursuit and a working memory task increased the diagnostic performance of pursuit metrics following mTBI. We integrated an n-back task with two levels of working memory load into a pursuit target, and tested single- and dual-task pursuit in mTBI patients and healthy controls. We assessed pursuit using measures of velocity accuracy, positional accuracy and positional variability. The mTBI group had higher pursuit variability than the control group in all conditions. Performing a concurrent 1-back task decreased pursuit variability for both the mTBI and control groups. Performing a concurrent 2-back task produced differential effects between the groups: Pursuit variability was significantly decreased in the control group, but not in the mTBI group. Diagnostic indices were improved when pursuit was combined with the 2-back task, and increased by 20% for the most sensitive variable. Smooth pursuit with simultaneous working memory load may be a superior diagnostic tool for mTBI than measuring smooth pursuit alone.

Shared variance of oculomotor phenotypes in a large sample of healthy young men

This study used canonical correlation analysis to investigate patterns of shared variance between parameters measured in seven different occulomotor function tasks, namely the visually guided saccade task, the antisaccade task, the closed-loop smooth-pursuit task, the open-loop smooth-pursuit task, and three active visual fixation tasks. These tasks were performed by 2130 young army recruits. Only a small percentage (1-10%) of shared variance existed between sets of parameters for all oculomotor function tasks measured. The most correlated tasks were the visually guided saccade and the antisaccade. The first common factor correlated with speed of performance between these tasks (latency), while the second and third correlated with accuracy of performance. Better performance in active visual fixation tasks correlated with better performance accuracy (lower error rate) and increased speed (lower latency) in the antisaccade and saccade tasks as well as better performance in the closed-loop smooth-pursuit task (increase in gain and decrease in the rate of unwanted saccades during pursuit). Better performance in the closed-loop smooth-pursuit task (increased gain and decreased number of unwanted saccades) also correlated with increased accuracy and increased speed of performing saccades and antisaccades. Finally, the open-loop fixation task had no correlation with all other oculomotor tasks except for a very weak negative correlation with the closed-loop pursuit task where better performance (increased gain) in one correlated with worse performance (decreased gain) in the other. The results of this analysis showed that a small percentage of variance is shared among different oculomotor function tasks. The structure of this shared variance could be used to derive common oculomotor function indices to study their relation to genetic and other sources of inter-subject variation.

Neuroticism, schizotypy, and scale anchors influence eye movement behaviour in the visual exploration of abstract art: An exploratory study

The same piece of artwork can attract both admiration and rejection from different people. One potential explanation for this effect is individual differences in perceptual biases, which influence the way in which we see different aspects of the same image. We explored the relationship between individual differences (i.e., personality) and eye movements for examinations of abstract art. Images were presented for 5000ms, after which participants judged aesthetic appeal and perceived value using visual analogue scales. Scale anchor labels (Looks Good/Looks Bad; $0/$5000) were counterbalanced between participants such that positive labels were on the left half of the time and on the right half of the time. Overall, more fixations occurred to the right and upper visual fields. Neuroticism significantly predicted the proportion of fixations to the left, whereas cognitive disorganisation negatively predicted the proportion of fixations to upper space. Participants found images more aesthetically pleasing and more valuable when positive anchors were on the left. Findings demonstrate that personality traits influence fixation patterns. Further, the positioning of positive anchor labels on the left leads to higher ratings of visual stimuli.

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.

Effects of ketamine on brain function during smooth pursuit eye movements

The uncompetitive NMDA receptor antagonist ketamine has been proposed to model symptoms of psychosis. Smooth pursuit eye movements (SPEM) are an established biomarker of schizophrenia. SPEM performance has been shown to be impaired in the schizophrenia spectrum and during ketamine administration in healthy volunteers. However, the neural mechanisms mediating SPEM impairments during ketamine administration are unknown. In a counter-balanced, placebo-controlled, double-blind, within-subjects design, 27 healthy participants received intravenous racemic ketamine (100 ng/mL target plasma concentration) on one of two assessment days and placebo (intravenous saline) on the other. Participants performed a block-design SPEM task during functional magnetic resonance imaging (fMRI) at 3 Tesla field strength. Self-ratings of psychosis-like experiences were obtained using the Psychotomimetic States Inventory (PSI). Ketamine administration induced psychosis-like symptoms, during ketamine infusion, participants showed increased ratings on the PSI dimensions cognitive disorganization, delusional thinking, perceptual distortion and mania. Ketamine led to robust deficits in SPEM performance, which were accompanied by reduced blood oxygen level dependent (BOLD) signal in the SPEM network including primary visual cortex, area V5 and the right frontal eye field (FEF), compared to placebo. A measure of connectivity with V5 and FEF as seed regions, however, was not significantly affected by ketamine. These results are similar to the deviations found in schizophrenia patients. Our findings support the role of glutamate dysfunction in impaired smooth pursuit performance and the use of ketamine as a pharmacological model of psychosis, especially when combined with oculomotor biomarkers. Hum Brain Mapp 37:4047-4060, 2016. © 2016 Wiley Periodicals, Inc.

Shared and distinct oculomotor function deficits in schizophrenia and obsessive compulsive disorder

Detailed analysis of oculomotor function phenotypes in antisaccade, smooth eye pursuit, and active fixation tasks was performed in a sample of 44 patients with schizophrenia, 34 patients with obsessive compulsive disorder (OCD), and 45 matched healthy controls. A common pattern of performance deficits in both schizophrenia and OCD emerged including higher antisaccade error rate, increased latency for corrective antisaccades, as well as higher rates of unwanted saccades in smooth eye pursuit compared to healthy controls. This common pattern could be related to the dysfunction of a network of cognitive control that is present in both disorders, including the dorsolateral prefrontal cortex, the posterior parietal cortex, and the anterior cingulate cortex. In contrast, only patients with schizophrenia showed a specific increase for correct antisaccade mean latency and the intrasubject variability of latency for error prosaccades as well as a decrease in the gain for smooth eye pursuit, suggesting a specific deficit in saccadic motor control and the frontal eye field in schizophrenia that is not present in OCD. A specific deficit in fixation stability (increased frequency of unwanted saccades during active fixation) was observed only for OCD patients pointing to a deficit in the frontostriatal network controlling fixation. This deficit was pronounced for OCD patients receiving additional antipsychotic medication. In conclusion, oculomotor function showed shared and distinct patterns of deviance for schizophrenia and OCD pointing toward shared and specific neurobiological substrates for these psychiatric disorders.

Individuals with pronounced schizotypal traits are particularly successful in tickling themselves

We assessed self-tickling sensations in a group of participants high in schizotypal traits (n=27) and group of participants low in schizotypal traits (n=27). The groups were formed by screening a pool of 397 students for extreme scores in the French version of the Schizotypal Personality Questionnaire. As observed in a previous study involving psychiatric people with auditory hallucinations and/or passivity experiences our results showed that self-applied tactile stimulations are felt to be more ticklish by healthy individuals high in schizotypal traits. In contrast, there were no significant intergroup differences in the mean tickle rating in the externally-produced tickling condition. Furthermore, more successful self-tickling was associated with more frequent self-reports of unusual perceptual experiences (such as supernatural experiences) and passivity experiences in particular (such as a feeling of being under the control of an outside force or power).

Neural mechanisms of smooth pursuit eye movements in schizotypy

Patients with schizophrenia as well as individuals with high levels of schizotypy are known to have deficits in smooth pursuit eye movements (SPEM). Here, we investigated, for the first time, the neural mechanisms underlying SPEM performance in high schizotypy. Thirty-one healthy participants [N = 19 low schizotypes, N = 12 high schizotypes (HS)] underwent functional magnetic resonance imaging at 3T with concurrent oculographic recording while performing a SPEM task with sinusoidal stimuli at two velocities (0.2 and 0.4 Hz). Behaviorally, a significant interaction between schizotypy group and velocity was found for frequency of saccades during SPEM, indicating impairments in HS in the slow but not the fast condition. On the neural level, HS demonstrated lower brain activation in different regions of the occipital lobe known to be associated with early sensory and attentional processing and motion perception (V3A, middle occipital gyrus, and fusiform gyrus). This group difference in neural activation was independent of target velocity. Together, these findings replicate the observation of altered pursuit performance in highly schizotypal individuals and, for the first time, identify brain activation patterns accompanying these performance changes. These posterior activation differences are compatible with evidence of motion processing deficits from the schizophrenia literature and, therefore, suggest overlap between schizotypy and schizophrenia both on cognitive-perceptual and neurophysiological levels. However, deficits in frontal motor areas observed during pursuit in schizophrenia were not seen here, suggesting the operation of additional genetic and/or illness-related influences in the clinical disorder.

Vergence eye movements in patients with schizophrenia

Previous studies have shown that smooth pursuit eye movements are impaired in patients with schizophrenia. However, under normal viewing conditions, targets move not only in the frontoparallel plane but also in depth, and tracking them requires both smooth pursuit and vergence eye movements. Although previous studies in humans and non-human primates suggest that these two eye movement subsystems are relatively independent of one another, to our knowledge, there have been no prior studies of vergence tracking behavior in patients with schizophrenia. Therefore, we have investigated these eye movements in patients with schizophrenia and in healthy controls. We found that patients with schizophrenia exhibited substantially lower gains compared to healthy controls during vergence tracking at all tested speeds (e.g. 0.25 Hz vergence tracking mean gain of 0.59 vs. 0.86). Further, consistent with previous reports, patients with schizophrenia exhibited significantly lower gains than healthy controls during smooth pursuit at higher target speeds (e.g. 0.5 Hz smooth pursuit mean gain of 0.64 vs. 0.73). In addition, there was a modest (r≈0.5), but significant, correlation between smooth pursuit and vergence tracking performance in patients with schizophrenia. Our observations clearly demonstrate substantial vergence tracking deficits in patients with schizophrenia. In these patients, deficits for smooth pursuit and vergence tracking are partially correlated suggesting overlap in the central control of smooth pursuit and vergence eye movements.

The effects of ketamine and risperidone on eye movement control in healthy volunteers

The non-competitive N-methyl-D-aspartate receptor antagonist ketamine leads to transient psychosis-like symptoms and impairments in oculomotor performance in healthy volunteers. This study examined whether the adverse effects of ketamine on oculomotor performance can be reversed by the atypical antipsychotic risperidone. In this randomized double-blind, placebo-controlled study, 72 healthy participants performed smooth pursuit eye movements (SPEM), prosaccades (PS) and antisaccades (AS) while being randomly assigned to one of four drug groups (intravenous 100 ng ml(-1) ketamine, 2 mg oral risperidone, 100  ng ml(-1) ketamine plus 2 mg oral risperidone, placebo). Drug administration did not lead to harmful adverse events. Ketamine increased saccadic frequency and decreased velocity gain of SPEM (all P < 0.01) but had no significant effects on PS or AS (all P > or = 0.07). An effect of risperidone was observed for amplitude gain and peak velocity of PS and AS, indicating hypometric gain and slower velocities compared with placebo (both P < or = 0.04). No ketamine by risperidone interactions were found (all P > or = 0.26). The results confirm that the administration of ketamine produces oculomotor performance deficits similar in part to those seen in schizophrenia. The atypical antipsychotic risperidone did not reverse ketamine-induced deteriorations. These findings do not support the cognitive enhancing potential of risperidone on oculomotor biomarkers in this model system of schizophrenia and point towards the importance of developing alternative performance-enhancing compounds to optimise pharmacological treatment of schizophrenia.

Schizotypal personality disorder

Early phenomenological descriptions of schizophrenia have acknowledged the existence of milder schizophrenia spectrum disorders characterized by the presence of attenuated symptoms typically present in chronic schizophrenia. The investigation of the schizophrenia spectrum disorders offers an opportunity to elucidate the pathophysiological mechanisms giving rise to schizophrenia. Differences and similarities between subjects with schizotypal personality disorder (SPD), the prototypical schizophrenia personality disorder, and chronic schizophrenia have been investigated with genetic, neurochemical, imaging, and pharmacological techniques. Patients with SPD and the more severely ill patients with chronic schizophrenia share cognitive, social, and attentional deficits hypothesized to result from common neurodevelopmentally based cortical temporal and prefrontal pathology. However, these deficits are milder in SPD patients due to their capacity to recruit other related brain regions to compensate for dysfunctional areas. Individuals with SPD are also less vulnerable to psychosis due to the presence of protective factors mitigating subcortical DA hyperactivity. Given the documented close relationship to other schizophrenic disorders, SPD will be included in the psychosis section of DSM-5 as a schizophrenia spectrum disorder as well as in the personality disorder section.

Eye-head coordination abnormalities in schizophrenia

BACKGROUND

Eye-movement abnormalities in schizophrenia are a well-established phenomenon that has been observed in many studies. In such studies, visual targets are usually presented in the center of the visual field, and the subject's head remains fixed. However, in every-day life, targets may also appear in the periphery. This study is among the first to investigate eye and head movements in schizophrenia by presenting targets in the periphery of the visual field.

METHODOLOGY/PRINCIPAL FINDINGS

Two different visual recognition tasks, color recognition and Landolt orientation tasks, were presented at the periphery (at a visual angle of 55° from the center of the field of view). Each subject viewed 96 trials, and all eye and head movements were simultaneously recorded using video-based oculography and magnetic motion tracking of the head. Data from 14 patients with schizophrenia and 14 controls were considered. The patients had similar saccadic latencies in both tasks, whereas controls had shorter saccadic latencies in the Landolt task. Patients performed more head movements, and had increased eye-head offsets during combined eye-head shifts than controls.

CONCLUSIONS/SIGNIFICANCE

Patients with schizophrenia may not be able to adapt to the two different tasks to the same extent as controls, as seen by the former's task-specific saccadic latency pattern. This can be interpreted as a specific oculomotoric attentional dysfunction and may support the hypothesis that schizophrenia patients have difficulties determining the relevance of stimuli. Patients may also show an uneconomic over-performance of head-movements, which is possibly caused by alterations in frontal executive function that impair the inhibition of head shifts. In addition, a model was created explaining 93% of the variance of the response times as a function of eye and head amplitude, which was only observed in the controls, indicating abnormal eye-head coordination in patients with schizophrenia.

Effects of risperidone, amisulpride and nicotine on eye movement control and their modulation by schizotypy

RATIONALE

The increasing demand to develop more efficient compounds to treat cognitive impairments in schizophrenia has led to the development of experimental model systems. One such model system combines the study of surrogate populations expressing high levels of schizotypy with oculomotor biomarkers.

OBJECTIVES

We aimed (1) to replicate oculomotor deficits in a psychometric schizotypy sample and (2) to investigate whether the expected deficits can be remedied by compounds shown to ameliorate impairments in schizophrenia.

METHODS

In this randomized double-blind, placebo-controlled study 233 healthy participants performed prosaccade (PS), antisaccade (AS) and smooth pursuit eye movement (SPEM) tasks after being randomly assigned to one of four drug groups (nicotine, risperidone, amisulpride, placebo). Participants were classified into medium- and high-schizotypy groups based on their scores on the Schizotypal Personality Questionnaire (SPQ, Raine (Schizophr Bull 17:555-564, 1991)).

RESULTS

AS error rate showed a main effect of Drug (p < 0.01), with nicotine improving performance, and a Drug by Schizotypy interaction (p = 0.04), indicating higher error rates in medium schizotypes (p = 0.01) but not high schizotypes under risperidone compared to placebo. High schizotypes had higher error rates than medium schizotypes under placebo (p = 0.03). There was a main effect of Drug for saccadic peak velocity and SPEM velocity gain (both p ≤ 0.01) indicating impaired performance with risperidone.

CONCLUSIONS

We replicate the observation of AS impairments in high schizotypy under placebo and show that nicotine enhances performance irrespective of group status. Caution should be exerted in applying this model as no beneficial effects of antipsychotics were seen in high schizotypes.

Smooth pursuit and visual occlusion: active inference and oculomotor control in schizophrenia

This paper introduces a model of oculomotor control during the smooth pursuit of occluded visual targets. This model is based upon active inference, in which subjects try to minimise their (proprioceptive) prediction error based upon posterior beliefs about the hidden causes of their (exteroceptive) sensory input. Our model appeals to a single principle – the minimisation of variational free energy – to provide Bayes optimal solutions to the smooth pursuit problem. However, it tries to accommodate the cardinal features of smooth pursuit of partially occluded targets that have been observed empirically in normal subjects and schizophrenia. Specifically, we account for the ability of normal subjects to anticipate periodic target trajectories and emit pre-emptive smooth pursuit eye movements – prior to the emergence of a target from behind an occluder. Furthermore, we show that a single deficit in the postsynaptic gain of prediction error units (encoding the precision of posterior beliefs) can account for several features of smooth pursuit in schizophrenia: namely, a reduction in motor gain and anticipatory eye movements during visual occlusion, a paradoxical improvement in tracking unpredicted deviations from target trajectories and a failure to recognise and exploit regularities in the periodic motion of visual targets. This model will form the basis of subsequent (dynamic causal) models of empirical eye tracking measurements, which we hope to validate, using psychopharmacology and studies of schizophrenia.

Schizophrenia-related RGS4 gene variations specifically disrupt prefrontal control of saccadic eye movements

BACKGROUND

The gene encoding the regulator of G-protein signaling subtype 4 (RGS4), located on chromosome 1q23-3, has been proposed as a possible susceptibility gene for schizophrenia and has been specifically linked to prefrontal cortical structural and functional integrity.

METHOD

The effects of four core single nucleotide polymorphisms (SNPs) within the RGS4 gene on oculomotor parameters in a battery of oculomotor tasks (saccade, antisaccade, smooth eye pursuit, fixation) were investigated in a sample of 2243 young male military conscripts.

RESULTS

The risk allele of RGS4SNP18 was found to be associated with two variables of antisaccade performance, increased error rate and variation in the correct antisaccade latency. By contrast, the same allele and also the risk allele of RGS4SNP4 led to an improvement in smooth eye pursuit performance (increased gain). Structural equation modeling confirmed that the combined gene variation of RGS4SNP4 and RGS4SNP18 was a significant predictor of antisaccade but not smooth eye pursuit performance.

CONCLUSIONS

These results provide evidence for a specific effect of schizophrenia-related RGS4 genotype variations to prefrontal dysfunction measured by oculomotor indices of performance in normal individuals, further validating the hypothesis that RGS4 is related to prefrontal dysfunction in schizophrenia.

Predictive smooth eye pursuit in a population of young men: II. Effects of schizotypy, anxiety and depression

Smooth pursuit eye movement dysfunction is considered to be a valid schizophrenia endophenotype. Recent studies have tried to refine the phenotype in order to identify the specific neurophysiological deficits associated with schizophrenia. We used a variation of the smooth eye pursuit paradigm, during which the moving target is occluded for a short period of time and subjects are asked to continue tracking. This is designed to isolate the predictive processes that drive the extraretinal signal, a process previously reported to be defective in schizophrenia patients as well as their healthy relatives. In the current study, we investigated the relationship between predictive pursuit performance indices and age, education, non-verbal IQ, schizotypy and state anxiety, depression in 795 young Greek military conscripts. State anxiety was related to better predictive pursuit performance (increase in residual pursuit gain), while disorganized schizotypy was related to deficient predictive pursuit performance (decreased residual gain). This effect was independent of the effect of disorganized schizotypy on other oculomotor functions supporting the hypothesis that predictive pursuit might be specifically affected in schizophrenia spectrum disorders and could be considered as a distinct oculomotor endophenotype.

Predictive smooth eye pursuit in a population of young men: I. Effects of age, IQ, oculomotor and cognitive tasks

Smooth eye pursuit is believed to involve the integration of an extraretinal signal formed by an internal representation of the moving target and a retinal signal using the visual feedback to evaluate performance. A variation of the smooth eye pursuit paradigm (in which the moving target is occluded for a short period of time and subjects are asked to continue tracking) designed to isolate the predictive processes that drive the extraretinal signal was performed by 1,187 young men. The latency to the onset of change in pursuit speed, the time of decelerating eye-movement speed and the steady state residual gain were measured for each subject and correlated with measures of other oculomotor (closed-loop smooth eye pursuit, saccade, antisaccade, active fixation) and cognitive tasks (measuring sustained attention and working memory). Deceleration time increased with increasing age, while education, general IQ and cognitive variables had no effect on predictive pursuit performance. Predictive pursuit indices were correlated to those of closed-loop pursuit and antisaccade performance, but these correlations were very weak except for a positive correlation of residual gain to saccade frequency in the fixation task with distracters. This correlation suggested that the maintenance of active fixation is negatively correlated with the ability to maintain predictive pursuit speed. In conclusion, this study presents predictive pursuit performance in a large sample of apparently healthy individuals. Surprisingly, predictive pursuit was weakly if at all related to closed-loop pursuit or other oculomotor and cognitive tasks, supporting the usefulness of this phenotype in the study of frontal lobe integrity in normal and patient populations.

A psychometric approach to the relationship between hand-foot preference and auditory hallucinations in the general population: atypical cerebral lateralization may cause an abnormal sense of agency

The present study examined the relationship between the atypical cerebral lateralization pattern represented in hand and foot preferences and schizotypal personality traits, especially proneness to auditory hallucinations as related to a sense of agency. A sense of agency, measured with questionnaires in the present study, is the sense that "I am the one who causes the actions." Although atypical lateralization and an abnormal sense of agency may be related to schizophrenia or schizotypal personality, the connection between them has remained unclear. The present study used cluster analysis to categorize the handedness-footedness combinations. The results indicated that people with right-handedness and left-footedness may have more schizotypal traits and that their abnormal sense of agency may cause schizotypal personality traits. Although the reasons for crossed lateral preference remain unclear, we discuss this in terms of early switching in handedness, which may underlie atypical lateralization and lead to the experience of auditory hallucinations deriving from an abnormal sense of agency.

Evaluation of state and trait biomarkers in healthy volunteers for the development of novel drug treatments in schizophrenia

Antipsychotic drugs are the mainstay of treatment for schizophrenia but they have little effect on core negative symptoms or cognitive impairment. To meet the deficiencies of current treatments, novel potential compounds are emerging from preclinical research but translation to clinical success has been poor. This article evaluates the possibility that cognitive and physiological abnormalities in schizophrenia can be used as central nervous system biomarkers to predict, in healthy volunteers, the likely efficacy of entirely new pharmacological approaches to treatment. Early detection of efficacy would focus resource on rapidly developing, effective drugs. We review the relevance of selected cognitive and physiological abnormalities as biomarkers in schizophrenia and three of its surrogate populations: (i) healthy volunteers with high trait schizotypy; (ii) unaffected relatives of patients; and (iii) healthy volunteers in a state of cortical glutamate disinhibition induced by low-dose ketamine. Several biomarkers are abnormal in these groups and in some instances there has been exploratory work to determine their sensitivity to drug action. They are generally insensitive to current antipsychotics and therefore their predictive validity cannot be established until novel, therapeutically useful drugs are discovered. Until then such biomarker studies can provide evidence of drugs engaging with the mechanism of interest and encouragement of the concept.

Schizophrenia-related neuregulin-1 single-nucleotide polymorphisms lead to deficient smooth eye pursuit in a large sample of young men

Neuregulin-1 (NRG1) variations have been shown to modulate schizophrenia candidate endophenotypes related to brain structure and function. The aim of this study was to determine the effect of NRG1 on several oculomotor schizophrenia endophenotypes. The effects of 5 core single-nucleotide polymorphisms (SNPs) within the NRG1 gene to oculomotor parameters in a battery of oculomotor tasks (saccade, antisaccade, smooth eye pursuit, fixation) were investigated in a sample of 2243 young male military conscripts. Additive regression models, bootstrap and permutation techniques, were used as well as structural equation modeling and haplotype analysis. A deficit in global smooth eye pursuit performance measured using the root-mean-square error (RMSE) was related to the risk allele of SNP8NRG243177, and a deficit in global smooth eye pursuit performance measured using the saccade frequency was related with the risk allele of SNP8NRG433E1006. Structural equation modeling confirmed a global effect of NRG1 genotype on smooth eye pursuit performance using the RMSE, while the effect on saccade frequency was not confirmed. Haplotype analysis further confirmed the prediction from the structural equation modeling that a combination of alleles corresponding to the Icelandic high-risk haplotype was related to a deficit in global pursuit performance. NRG1 genotype variations were related to smooth eye pursuit variations both at the SNP level and at the haplotype level adding to the validation of this gene as a candidate gene for the disorder.

Psychophysiological markers of vulnerability to psychopathology in men with an extra X chromosome (XXY)

Studying genetically defined syndromes associated with increased risk for psychopathology may help in understanding neurodevelopmental mechanisms related to risk for psychopathology. Klinefelter syndrome (47,XXY) is one of the most common sex chromosomal aneuploidies (1 in 650 male births) and associated with increased vulnerability for psychopathology, including psychotic symptoms. Yet, it remains unknown whether this increased risk is associated with underlying psychophysiological mechanisms that are typically deficient in individuals with psychotic disorders. The present study assessed three “classic” psychophysiological markers of psychosis in Klinefelter syndrome (KS): smooth pursuit eye movements (SPEM), prepulse inhibition (PPI) and P50 suppression. Fourteen adults with KS and 15 non-clinical adults participated in the study. Data on SPEM (reflecting visuo-motor control) as well as PPI and P50 suppression (reflecting sensory gating) were collected. Dysfunctions in SPEM were observed in individuals with KS, with less smooth pursuit as expressed in lower position gain. Also, reduced sensory gating in individuals with KS was suggested by significantly reduced prepulse inhibition of the startle response (PPI) (effect size 1.6). No abnormalities were found in suppression of the P50 (effect size 0.6). We speculate that impairments in these psychophysiological mechanisms may reflect core brain dysfunctions that may also mediate the described increased vulnerability for psychotic symptoms in KS. Although speculative, such deficit specific, rather than disorder specific, psychophysiological dysfunctions in KS might convey vulnerability to other types of psychopathology as well. As KS already can be diagnosed prenatally, the predictive value of childhood impairments in prepulse inhibition and smooth pursuit for development of psychopathology later in life could be assessed. In sum, studying individuals with KS may prove to be an avenue of research leading to new hypotheses and insights into “at risk” pathways to psychopathology.

The hierarchic structure in schizotypy and the five-factor model of personality

Schizotypal personality traits (schizotypy) might be seen as on a continuum with schizophrenia. However, controversy remains with regard to whether this continuum is quasi-dimensional, applying only to people with schizophrenia and schizotypy, or fully dimensional, applying to all people. If the fully dimensional model is accurate, schizotypy could be described by the same personality theories as are applied to people in general. We examined the relationship between schizotypy and the five-factor model of personality (FFM), which is arguably the most established contemporary personality theory. When we assumed a hierarchic structure of schizotypy factors, we found that the FFM scales could explain schizotypy fairly well regardless of the questionnaires used, suggesting that schizotypy might represent a variation better understood by reference to typical dimensions of personality, though it might still indicate a predisposition to schizophrenia. This article discusses this conclusion in relation to each of the five personality factors. A perspective that situates schizophrenia on a continuum with general personality variations implies that this disorder constitutes a potential risk for everyone and, thus, helps to promote understanding and correct misunderstandings that contribute to prejudice.

SPEM dysfunction and general schizotypy as measured by the SSQ: a controlled study

Background

SPEM dysfunction is a well-known phenomenon in schizophrenia. The principal aim of the present study was to examine whether SPEM dysfunction is already observable in subjects scoring high on a specific measure of schizotypy (SSQ General Schizotypy) that was selected because of its intimate relationship with schizophrenic prodromal unfolding.

Methods

Applying ANOVAs, we determined the relationship of subjects' scores on SSQ General Schizotypy and eye movements elicited by targets of different speed. We also examined whether there exists an association between our schizotypy measure and pupil size.

Results

We found more SPEM dysfunction in subjects scoring high on SSQ General Schizotypy than in subjects scoring average on that factor, irrespective of the speed of the target. No relationship was found between baseline pupil size and General Schizotypy.

Conclusion

The present study provides additional evidence that SPEM dysfunction is associated with schizotypic features that precede the onset of schizophrenia and is already observable in general population subjects that show these features.

Schizotypal personality traits and atypical lateralization in motor and language functions

Atypical cerebral lateralization in motor and language functions in regard to schizotypal personality traits in healthy populations, as well as among schizophrenic patients, has attracted attention because these traits may represent a risk factor for schizophrenia. Although the relationship between handedness and schizotypal personality has been widely examined, few studies have adopted an experimental approach. This study consisted of three experiments focusing on motor and language functional lateralization in regard to schizotypal personality in the absence of mental illness: line-drawing, finger tapping, and a semantic go/no-go task. The results suggested that positive schizotypal personality might be related to functional non-lateralization in regard to at least some functions (e.g., spatial motor control and semantic processing in the present study). Subjects with high schizotypal personality traits performed equally with their right and left-hands in the line-drawing task and they reacted equally with their right and left-hands in a semantic go/no-go task involving semantic auditory stimuli presented in both ears. However, those low in schizotypal personality traits showed typical lateralization in response to these tasks. We discuss the implications of these findings for schizotypal atypical lateralization.

The effect of change in clinical state on eye movement dysfunction in schizophrenia

Measures of eye movement dysfunction have been considered as candidate endophenotypes for the study of genetic liability in schizophrenia. In this respect it is crucial to confirm a clinical state independentce of these measures. Twenty people with DSM-IV schizophrenia were assessed using a battery of oculomotor tasks in the acute phase of their disorder without being treated with antipsychotic medication and then again in the remission phase under treatment with antipsychotic medication. The saccade latency in the saccade task, the error rate and antisaccade latency in the antisaccade task, and the frequency of unwanted saccades in the active fixation task were stable in time both at the group level and within each individual, showing no relation to the significant improvement in different psychopathological dimensions of these patients. The root mean square error, gain and saccade frequency in the pursuit task were not stable over time, although again this instability was not related to the changes in psychopathological status of these patients. Finally, the saccade frequency in the active fixation task with distracters was not stable in time and was correlated with changes in specific dimensions of psychopathology. These results provide further evidence that saccade and smooth eye pursuit dysfunction measures are not affected by the substantial change in the clinical state of schizophrenia from the acute phase to remission, and strengthen the current view that they can be used as endophenotypes. On the other hand, active fixation might be state-dependent adding to the evidence against its use as a candidate endophenotype in schizophrenia.

A review on eye movement studies in childhood and adolescent psychiatry

The neural substrates of eye movement measures are largely known. Therefore, measurement of eye movements in psychiatric disorders may provide insight into the underlying neuropathology of these disorders. Visually guided saccades, antisaccades, memory guided saccades, and smooth pursuit eye movements will be reviewed in various childhood psychiatric disorders. The four aims of this review are (1) to give a thorough overview of eye movement studies in a wide array of psychiatric disorders occurring during childhood and adolescence (attention-deficit/hyperactivity disorder, oppositional deviant disorder and conduct disorder, autism spectrum disorders, reading disorder, childhood-onset schizophrenia, Tourette's syndrome, obsessive compulsive disorder, and anxiety and depression), (2) to discuss the specificity and overlap of eye movement findings across disorders and paradigms, (3) to discuss the developmental aspects of eye movement abnormalities in childhood and adolescence psychiatric disorders, and (4) to present suggestions for future research. In order to make this review of interest to a broad audience, attention will be given to the clinical manifestation of the disorders and the theoretical background of the eye movement paradigms.

Physiology and pathology of eye–head coordination

Human head movement control can be considered as part of the oculomotor system since the control of gaze involves coordination of the eyes and head. Humans show a remarkable degree of flexibility in eye-head coordination strategies, nonetheless an individual will often demonstrate stereotypical patterns of eye-head behaviour for a given visual task. This review examines eye-head coordination in laboratory-based visual tasks, such as saccadic gaze shifts and combined eye-head pursuit, and in common tasks in daily life, such as reading. The effect of the aging process on eye-head coordination is then reviewed from infancy through to senescence. Consideration is also given to how pathology can affect eye-head coordination from the lowest through to the highest levels of oculomotor control, comparing conditions as diverse as eye movement restrictions and schizophrenia. Given the adaptability of the eye-head system we postulate that this flexible system is under the control of the frontal cortical regions, which assist in planning, coordinating and executing behaviour. We provide evidence for this based on changes in eye-head coordination dependant on the context and expectation of presented visual stimuli, as well as from changes in eye-head coordination caused by frontal lobe dysfunction.