Specific motion processing pathway deficit during eye tracking in schizophrenia: a performance-matched functional magnetic resonance imaging study

Disrupted third visual pathway function in schizophrenia: Evidence from real and implied motion processing

Impaired motion perception in schizophrenia has been associated with deficits in social-cognitive processes and with reduced activation of visual sensory regions, including the middle temporal area (MT+) and posterior superior temporal sulcus (pSTS). These findings are consistent with the recent proposal of the existence of a specific 'third visual pathway' specialized for social perception in which motion is a fundamental component. The third visual pathway transmits visual information from early sensory visual processing areas to the STS, with MT+ acting as a critical intermediary. We used functional magnetic resonance imaging to investigate functioning of this pathway during processing of naturalistic videos with explicit (real) motion and static images with implied motion cues. These measures were related to face emotion recognition and motion-perception, as measured behaviorally. Participants were 28 individuals with schizophrenia (Sz) and 20 neurotypical controls. Compared to controls, individuals with Sz showed reduced activation of third visual pathway regions (MT+, pSTS) in response to both real- and implied-motion stimuli. Dysfunction of early visual cortex and pulvinar were also associated with aberrant real-motion processing. Implied-motion stimuli additionally engaged a wide network of brain areas including parietal, motor and frontal nodes of the human mirror neuron system. The findings support concepts of MT+ as a mediator between visual sensory areas and higher-order brain and argue for greater focus on MT+ contributions to social-cognitive processing, in addition to its well-documented role in visual motion processing.

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.

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.

Disrupted Corollary Discharge in Schizophrenia: Evidence From the Oculomotor System

Corollary discharge (CD) signals are motor-related signals that exert an influence on sensory processing. They allow mobile organisms to predict the sensory consequences of their imminent actions. Among the many functions of CD is to provide a means by which we can distinguish sensory experiences caused by our own actions from those with external causes. In this way, they contribute to a subjective sense of agency. A disruption in the sense of agency is central to many of the clinical symptoms of schizophrenia, and abnormalities in CD signaling have been theorized to underpin particularly those agency-related psychotic symptoms of the illness. Characterizing abnormal CD associated with eye movements in schizophrenia and their resulting influence on visual processing and subsequent action plans may have advantages over other sensory and motor systems. That is because the most robust psychophysiological and neurophysiological data regarding the dynamics and influence of CD as well as the neural circuitry implicated in CD generation and transmission comes from the study of eye movements in humans and nonhuman primates. We review studies of oculomotor CD signaling in the schizophrenia spectrum and possible neurobiological correlates of CD disturbances. We conclude by speculating on the ways in which oculomotor CD dysfunction, specifically, may invoke specific experiences, clinical symptoms, and cognitive impairments. These speculations lay the groundwork for empirical study, and we conclude by outlining potentially fruitful research directions.

Cannabis use and human retina: The path for the study of brain synaptic transmission dysfunctions in cannabis users

Owing to the difficulty of obtaining direct access to the functioning brain, new approaches are needed for the indirect exploration of brain disorders in neuroscience research. Due to its embryonic origin, the retina is part of the central nervous system and is well suited to the investigation of neurological functions in psychiatric and addictive disorders. In this review, we focus on cannabis use, which is a crucial public health challenge, since cannabis is one of the most widely used addictive drugs in industrialized countries. We first explain why studying retinal function is relevant when exploring the effects of cannabis use on brain function. Next, we describe both the retinal electrophysiological measurements and retinal dysfunctions observed after acute and regular cannabis use. We then discuss how these retinal dysfunctions may inform brain synaptic transmission abnormalities. Finally, we present various directions for future research on the neurotoxic effects of cannabis use.

Resting-state functional magnetic resonance imaging (fMRI) and functional connectivity density mapping in patients with corneal ulcer

PURPOSE

To investigate alternations in spontaneous brain activities reflected by functional connectivity density (FCD) in patients with corneal ulcer (CU) using resting-state functional connectivity (rsFC).

METHODS

We recruited 24 patients with CU (12 males, 12 females), and 24 healthy controls (HCs; 12 males, 12 females) matched for age, gender and education status. Functional magnetic resonance imaging examinations were performed on all subjects in a resting state and the following parameters determined: rsFC, long-range FCD (longFCD) and short-range FCD (IFCD). Receiver operating characteristic (ROC) curves were then used to differentiate patients with CU from HCs.

RESULTS

Compared with HCs, CU patients showed significantly reduced rsFC values in the right cerebellum posterior lobe gyrus, right middle frontal gyrus/inferior frontal gyrus/superior frontal gyrus and left inferior parietal lobule/precuneus. Significantly reduced longFCD values were found in the right hippocampus/inferior temporal gyrus and the left inferior temporal gyrus. Moreover, compared with HCs, IFCD values were significantly reduced in the left inferior temporal gyrus/middle temporal gyrus, left limbic lobe/medial frontal gyrus, and left precuneus/limbic lobe, but were significantly increased in the right insula/superior temporal gyrus, left superior temporal gyrus/inferior frontal gyrus/insula, right superior temporal gyrus/postcentral gyrus, and left precentral gyrus.

CONCLUSIONS

Patients with CU exhibited alterations in spontaneous brain activities in several brain areas. These novel findings may help to reveal the neuropathological mechanisms underlying CU.

This study provides a direction for further exploration of underlying neural mechanisms of CU and facilitate the clinical diagnosis and treatment of CU.

Multiple Frequency Bands Analysis of Large Scale Intrinsic Brain Networks and Its Application in Schizotypal Personality Disorder

The human brain is a complex system composed by several large scale intrinsic networks with distinct functions. The low frequency oscillation (LFO) signal of blood oxygen level dependent (BOLD), measured through resting-state fMRI, reflects the spontaneous neural activity of these networks. We propose to characterize these networks by applying the multiple frequency bands analysis (MFBA) to the LFO time courses (TCs) resulted from the group independent component analysis (ICA). Specifically, seven networks, including the default model network (DMN), dorsal attention network (DAN), control executive network (CEN), salience network, sensorimotor network, visual network and limbic network, are identified. After the power spectral density (PSD) analysis, the amplitude of low frequency fluctuation (ALFF) and the fractional amplitude of low frequency fluctuation (fALFF) is determined in three bands: <0.1 Hz; slow-5; and slow-4. Moreover, the MFBA method is applied to reveal the frequency-dependent alternations of fALFF for seven networks in schizotypal personality disorder (SPD). It is found that seven networks can be divided into three categories: the advanced cognitive networks, primary sensorimotor networks and limbic networks, and their fALFF successively decreases in both slow-4 and slow-5 bands. Comparing to normal control group, the fALFF of DMN, DAN and CEN in SPD tends to be higher in slow-5 band, but lower in slow-4. Higher fALFF of sensorimotor and visual networks in slow-5, higher fALFF of limbic network in both bands have been observed for SPD group. The results of ALFF are consistent with those of fALFF. The proposed MFBA method may help distinguish networks or oscillators in the human brain, reveal subtle alternations of networks through locating their dominant frequency band, and present potential to interpret the neuropathology disruptions.

Reading deficits in schizophrenia and their relationship to developmental dyslexia: A review

Although schizophrenia and developmental dyslexia are considered distinct disorders in terms of clinical presentation and functional outcome, they both involve disruption in the processes that support skilled reading, including language, auditory perception, visual perception, oculomotor control, and executive function. Further, recent work has proposed a common neurodevelopmental basis for the two disorders, as suggested by genetic and pathophysiological overlap. Thus, these lines of research suggest that reading may be similarly impacted in schizophrenia and dyslexia. In this review, we survey research on reading abilities in individuals with schizophrenia, and review the potential mechanisms underlying reading deficits in schizophrenia that may be shared with those implicated in dyslexia. Elucidating the relationship between reading impairment in schizophrenia and dyslexia could allow for a better understanding of the pathophysiological underpinnings of schizophrenia, and could facilitate remediation of cognitive deficits that impact day-to-day functioning.

Targeting neuronal dysfunction in schizophrenia with nicotine: Evidence from neurophysiology to neuroimaging

Patients with schizophrenia self-administer nicotine at rates higher than is self-administered for any other psychiatric illness. Although the reasons are unclear, one hypothesis suggests that nicotine is a form of 'self-medication' in order to restore normal levels of nicotinic signaling and target abnormalities in neuronal function associated with cognitive processes. This brief review discusses evidence from neurophysiological and neuroimaging studies in schizophrenia patients that nicotinic agonists may effectively target dysfunctional neuronal circuits in the illness. Evidence suggests that nicotine significantly modulates a number of these circuits, although relatively few studies have used modern neuroimaging techniques (e.g. functional magnetic resonance imaging (fMRI)) to examine the effects of nicotinic drugs on disease-related neurobiology. The neuronal effects of nicotine and other nicotinic agonists in schizophrenia remain a priority for psychiatry research.

Transsaccadic Perception Deficits in Schizophrenia Reflect the Improper Internal Monitoring of Eye Movement Rather Than Abnormal Sensory Processing

BACKGROUND

Symptoms of psychosis in schizophrenia reflect disturbances in sense of agency-difficulty distinguishing internally from externally generated sensory and perceptual experiences. One theory attributes these anomalies to a disruption in corollary discharge (CD), an internal copy of generated motor commands used to distinguish self-movement-generated sensations from externally generated stimulation.

METHODS

We used a transsaccadic shift detection paradigm to examine possible deficits in CD and sense of agency based on the ability to perceive visual changes in 31 schizophrenia patients (SZPs) and 31 healthy control subjects. We derived perceptual measures based on manual responses indicating the transsaccadic target shift direction. We also developed a distance-from-unity-line measure to quantify use of CD versus purely sensory (visual) information in evaluating visual changes in the environment after an eye movement.

RESULTS

SZPs had higher perceptual thresholds in detecting shift of target location than healthy control subjects, regardless of movement direction or amplitude. Despite producing similar hypometric saccades, healthy control subjects overestimated target location, whereas SZPs relied more on the experienced visual error and consequently underestimated the target position. We show that in SZPs the postsaccadic judgment of the initial target location was largely aligned with the measure based only on visual error, suggesting a deficit in the use of CD. This CD deficit also correlated with positive schizophrenia symptoms and disturbances in sense of agency.

CONCLUSIONS

These results provide a novel approach in quantifying abnormal use of CD in SZPs and provide a framework to distinguish deficits in sensory processing versus defects in the internal CD-based monitoring of movement.

Oculomotor Prediction: A Window into the Psychotic Mind

Psychosis - an impaired contact with reality - is a hallmark of schizophrenia. Many psychotic symptoms are associated with disruptions in agency - the sense that 'I' cause my actions. A failure to predict sensory consequences of one's own actions may underlie agency disturbances. Such predictions rely on corollary discharge (CD) signals, 'copies' of movement commands sent to sensory regions prior to action execution. Here, we make a case that the oculomotor system is a promising model for understanding CD in psychosis, building on advances in our understanding of the behavioral and neurophysiological correlates of CD associated with eye movements. In this opinion article, we provide an overview of recent evidence for disturbed oculomotor CD in schizophrenia, potentially linking bizarre and disturbing psychotic experiences with basic physiological processes.

Visual and non-visual motion information processing during pursuit eye tracking in schizophrenia and bipolar disorder

Despite many reports on visual processing deficits in psychotic disorders, studies are needed on the integration of visual and non-visual components of eye movement control to improve the understanding of sensorimotor information processing in these disorders. Non-visual inputs to eye movement control include prediction of future target velocity from extrapolation of past visual target movement and anticipation of future target movements. It is unclear whether non-visual input is impaired in patients with schizophrenia. We recorded smooth pursuit eye movements in 21 patients with schizophrenia spectrum disorder, 22 patients with bipolar disorder, and 24 controls. In a foveo-fugal ramp task, the target was either continuously visible or was blanked during movement. We determined peak gain (measuring overall performance), initial eye acceleration (measuring visually driven pursuit), deceleration after target extinction (measuring prediction), eye velocity drifts before onset of target visibility (measuring anticipation), and residual gain during blanking intervals (measuring anticipation and prediction). In both patient groups, initial eye acceleration was decreased and the ability to adjust eye acceleration to increasing target acceleration was impaired. In contrast, neither deceleration nor eye drift velocity was reduced in patients, implying unimpaired non-visual contributions to pursuit drive. Disturbances of eye movement control in psychotic disorders appear to be a consequence of deficits in sensorimotor transformation rather than a pure failure in adding cognitive contributions to pursuit drive in higher-order cortical circuits. More generally, this deficit might reflect a fundamental imbalance between processing external input and acting according to internal preferences.

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.

Revisiting visual dysfunctions in schizophrenia from the retina to the cortical cells: A manifestation of defective neurodevelopment

This review highlights morphological and functional anomalies found along the entire visual pathway in schizophrenia, from the retina to the cortex. Based on the evidence of widespread anatomical and functional visual abnormalities, we posited that a neurodevelopmental anomaly occurring early in life was likely to explain those. Incidentally, support to the neurodevelopmental theory of schizophrenia is strongly emerging from many neurobiological domains. In vertebrates, the first visual structures migrate toward the orbit position at the end of the fourth week of gestation. A neurodevelopmental defect around that time on these embryonic structures could account for the visual anomalies in schizophrenia. Retinol activity might be involved in the process. Future research in schizophrenia should focus on early visual testing, on trials combining multiple visual anomaly assessments and a closer look to retinol activity during the pregnancy.

Ophthalmology issues in schizophrenia

Schizophrenia is a complex mental disorder associated with not only cognitive dysfunctions, such as memory and attention deficits, but also changes in basic sensory processing. Although most studies on schizophrenia have focused on disturbances in higher-order brain functions associated with the prefrontal cortex or frontal cortex, recent investigations have also reported abnormalities in low-level sensory processes, such as the visual system. At very early stages of the disease, schizophrenia patients frequently describe in detail symptoms of a disturbance in various aspects of visual perception that may lead to worse clinical symptoms and decrease in quality of life. Therefore, the aim of this review is to describe the various studies that have explored the visual issues in schizophrenia.

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.

Smooth pursuit eye movements and schizophrenia: literature review

OBJECTIVE

To review the scientific literature about the relationship between impairment on smooth pursuit eye movements and schizophrenia.

METHODS

Narrative review that includes historical articles, reports about basic and clinical investigation, systematic reviews, and meta-analysis on the topic.

RESULTS

Up to 80% of schizophrenic patients have impairment of smooth pursuit eye movements. Despite the diversity of test protocols, 65% of patients and controls are correctly classified by their overall performance during this pursuit. The smooth pursuit eye movements depend on the ability to anticipate the target's velocity and the visual feedback, as well as on learning and attention. The neuroanatomy implicated in smooth pursuit overlaps to some extent with certain frontal cortex zones associated with some clinical and neuropsychological characteristics of the schizophrenia, therefore some specific components of smooth pursuit anomalies could serve as biomarkers of the disease. Due to their sedative effect, antipsychotics have a deleterious effect on smooth pursuit eye movements, thus these movements cannot be used to evaluate the efficacy of the currently available treatments.

CONCLUSION

Standardized evaluation of smooth pursuit eye movements on schizophrenia will allow to use specific aspects of that pursuit as biomarkers for the study of its genetics, psychopathology, or neuropsychology.

Kalman filtering naturally accounts for visually guided and predictive smooth pursuit dynamics

The brain makes use of noisy sensory inputs to produce eye, head, or arm motion. In most instances, the brain combines this sensory information with predictions about future events. Here, we propose that Kalman filtering can account for the dynamics of both visually guided and predictive motor behaviors within one simple unifying mechanism. Our model relies on two Kalman filters: (1) one processing visual information about retinal input; and (2) one maintaining a dynamic internal memory of target motion. The outputs of both Kalman filters are then combined in a statistically optimal manner, i.e., weighted with respect to their reliability. The model was tested on data from several smooth pursuit experiments and reproduced all major characteristics of visually guided and predictive smooth pursuit. This contrasts with the common belief that anticipatory pursuit, pursuit maintenance during target blanking, and zero-lag pursuit of sinusoidally moving targets all result from different control systems. This is the first instance of a model integrating all aspects of pursuit dynamics within one coherent and simple model and without switching between different parallel mechanisms. Our model suggests that the brain circuitry generating a pursuit command might be simpler than previously believed and only implement the functional equivalents of two Kalman filters whose outputs are optimally combined. It provides a general framework of how the brain can combine continuous sensory information with a dynamic internal memory and transform it into motor commands.

Neural effects of auditory distraction on visual attention in schizophrenia

Sensory flooding, particularly during auditory stimulation, is a common problem for patients with schizophrenia. The functional consequences of this impairment during cross-modal attention tasks, however, are unclear. The purpose of this study was to examine how auditory distraction differentially affects task-associated response during visual attention in patients and healthy controls. To that end, 21 outpatients with schizophrenia and 23 healthy comparison subjects performed a visual attention task in the presence or absence of distracting, environmentally relevant "urban" noise while undergoing functional magnetic resonance imaging at 3T. The task had two conditions (difficult and easy); task-related neural activity was defined as difficult - easy. During task performance, a significant distraction (noise or silence) by group (patient or control) interaction was observed in the left dorsolateral prefrontal cortex, right hippocampus, left temporoparietal junction, and right fusiform gyrus, with patients showing relative hypoactivation during noise compared to controls. In patients, the ability to recruit the dorsolateral prefrontal cortex during the task in noise was negatively correlated with the effect of noise on reaction time. Clinically, the ability to recruit the fusiform gyrus during the task in noise was negatively correlated with SANS affective flattening score, and hippocampal recruitment during the task in noise was positively correlated with global functioning. In conclusion, schizophrenia may be associated with abnormalities in neural response during visual attention tasks in the presence of cross-modal noise distraction. These response differences may predict global functioning in the illness, and may serve as a biomarker for therapeutic development.

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.

Altered velocity processing in schizophrenia during pursuit eye tracking

Smooth pursuit eye movements (SPEM) are needed to keep the retinal image of slowly moving objects within the fovea. Depending on the task, about 50%-80% of patients with schizophrenia have difficulties in maintaining SPEM. We designed a study that comprised different target velocities as well as testing for internal (extraretinal) guidance of SPEM in the absence of a visual target. We applied event-related fMRI by presenting four velocities (5, 10, 15, 20°/s) both with and without intervals of target blanking. 17 patients and 16 healthy participants were included. Eye movements were registered during scanning sessions. Statistical analysis included mixed ANOVAs and regression analyses of the target velocity on the Blood Oxygen Level Dependency (BOLD) signal. The main effect group and the interaction of velocity×group revealed reduced activation in V5 and putamen but increased activation of cerebellar regions in patients. Regression analysis showed that activation in supplementary eye field, putamen, and cerebellum was not correlated to target velocity in patients in contrast to controls. Furthermore, activation in V5 and in intraparietal sulcus (putative LIP) bilaterally was less strongly correlated to target velocity in patients than controls. Altered correlation of target velocity and neural activation in the cortical network supporting SPEM (V5, SEF, LIP, putamen) implies impaired transformation of the visual motion signal into an adequate motor command in patients. Cerebellar regions seem to be involved in compensatory mechanisms although cerebellar activity in patients was not related to target velocity.

Altered transfer of visual motion information to parietal association cortex in untreated first-episode psychosis: implications for pursuit eye tracking

Visual motion processing and its use for pursuit eye movement control represent a valuable model for studying the use of sensory input for action planning. In psychotic disorders, alterations of visual motion perception have been suggested to cause pursuit eye tracking deficits. We evaluated this system in functional neuroimaging studies of untreated first-episode schizophrenia (N=24), psychotic bipolar disorder patients (N=13) and healthy controls (N=20). During a passive visual motion processing task, both patient groups showed reduced activation in the posterior parietal projection fields of motion-sensitive extrastriate area V5, but not in V5 itself. This suggests reduced bottom-up transfer of visual motion information from extrastriate cortex to perceptual systems in parietal association cortex. During active pursuit, activation was enhanced in anterior intraparietal sulcus and insula in both patient groups, and in dorsolateral prefrontal cortex and dorsomedial thalamus in schizophrenia patients. This may result from increased demands on sensorimotor systems for pursuit control due to the limited availability of perceptual motion information about target speed and tracking error. Visual motion information transfer deficits to higher-level association cortex may contribute to well-established pursuit tracking abnormalities, and perhaps to a wider array of alterations in perception and action planning in psychotic disorders.

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.

Downregulated kynurenine 3-monooxygenase gene expression and enzyme activity in schizophrenia and genetic association with schizophrenia endophenotypes

CONTEXT

Kynurenic acid, a metabolite of the kynurenine pathway of tryptophan degradation, is an antagonist at N-methyl-d-aspartate and α7 nicotinic acetylcholine receptors and modulates glutamate, dopamine, and acetylcholine signaling. Cortical kynurenic acid concentrations are elevated in the brain and cerebrospinal fluid of schizophrenia patients. The proximal cause may be an impairment of kynurenine 3-monooxygenase (KMO), a rate-limiting enzyme at the branching point of the kynurenine pathway.

OBJECTIVES

To examine KMO messenger RNA expression and KMO enzyme activity in postmortem tissue from the frontal eye field (FEF; Brodmann area 6) obtained from schizophrenia individuals compared with healthy control individuals and to explore the relationship between KMO single-nucleotide polymorphisms and schizophrenia oculomotor endophenotypes.

DESIGN

Case-control postmortem and clinical study.

SETTING

Maryland Brain Collection, outpatient clinics.

PARTICIPANTS

Postmortem specimens from schizophrenia patients (n = 32) and control donors (n = 32) and a clinical sample of schizophrenia patients (n = 248) and healthy controls (n = 228).

MAIN OUTCOME MEASURES

Comparison of quantitative KMO messenger RNA expression and KMO enzyme activity in postmortem FEF tissue between schizophrenia patients and controls and association of KMO single-nucleotide polymorphisms with messenger RNA expression in postmortem FEF and schizophrenia and oculomotor endophenotypes (ie, smooth pursuit eye movements and oculomotor delayed response).

RESULTS

In postmortem tissue, we found a significant and correlated reduction in KMO gene expression and KMO enzyme activity in the FEF in schizophrenia patients. In the clinical sample, KMO rs2275163 was not associated with a diagnosis of schizophrenia but showed modest effects on predictive pursuit and visuospatial working memory endophenotypes.

CONCLUSION

Our results provide converging lines of evidence implicating reduced KMO activity in the etiopathophysiology of schizophrenia and related neurocognitive deficits.

Abnormal visual motion processing in schizophrenia: a review of research progress

Motion processing represents a perceptual domain in which dynamic visual information is encoded to support the perception of movement. Research over the last decade has found a variety of abnormalities in the processing of motion information in schizophrenia. The abnormalities span from discrimination of basic motion features (such as speed) to integration of spatially distributed motion signals (such as coherent motion). Motion processing involves visual signals across space and time and thus presents a special opportunity to examine how spatial and temporal information is integrated in the visual system. This article surveys the behavioral and neuroimaging studies that probe into the spatial integration of motion information in schizophrenia. An emerging theme from these studies points to an imbalanced regulation of spatial interaction processes as a potential mechanism mediating different levels of abnormal motion processing in schizophrenia. The synthesis of these mechanism-driven studies suggests that further investigation of the neural basis and functional consequences of this abnormal motion processing are needed in order to render a basic biomarker for assessment and intervention of cognitive dysfunction in this mental disorder.

Abnormal neural oscillations in schizotypy during a visual working memory task: support for a deficient top-down network?

Neural oscillatory deficits have been proposed to be a core feature of schizophrenia spectrum disorders. In this study we aimed to confirm this by examining early evoked oscillatory patterns in the EEG theta, beta and gamma bands in individuals with high schizotypal personality trait scores. We carried out an event-related experiment using a computerised delayed matching to sample working memory (WM) task on a sample of volunteers scoring high or low on the Schizotypal Personality Questionnaire (SPQ). Phase-locking factor (PLF), a measure of network synchronisation, was reduced in the beta and gamma bands in two distinct topographical regions (fronto-central and centraloccipital). In addition, signal power in the beta band was decreased in the high schizotypy group in the same fronto-occipital network. These findings suggest that abnormalities in functional connectivity, already described in schizophrenia, extend to schizotypy. Further, the pattern and latency of the altered neural oscillations in the high schizotypy group suggests a deficient modulation of the sensory processing by higher-order structures. Such top-down deficits have been reported in schizophrenia and this data supports the idea that top-down dysfunction is a vulnerability trait that is independent of disease course, medication or symptom severity.

Response inhibition and response monitoring in a saccadic countermanding task in schizophrenia

BACKGROUND

Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and are reliable predictors of functional outcome, but the specificity of these deficits and their underlying neural mechanisms have not been fully elucidated. The objective of the present study was to determine the nature of response inhibition and response monitoring deficits in SZ and their relationship to symptoms and social and occupational functioning with a behavioral paradigm that provides a translational approach to investigating cognitive control.

METHODS

Seventeen patients with SZ and 16 demographically matched healthy control subjects participated in a saccadic countermanding task. Performance on this task is approximated as a race between movement generation and inhibition processes; this race model provides an estimate of the time needed to cancel a planned movement. Response monitoring can be assessed by reaction time adjustments on the basis of trial history.

RESULTS

Saccadic reaction time was normal, but patients required more time to inhibit a planned saccade. The latency of the inhibitory process was associated with the severity of negative symptoms and poorer occupational functioning. Both groups slowed down significantly after correctly cancelled and erroneously noncancelled stop signal trials, but patients slowed down more than control subjects after correctly inhibited saccades.

CONCLUSIONS

These results suggest that SZ is associated with a difficulty in inhibiting planned movements and an inflated response adjustment effect after inhibiting a saccade. Furthermore, behavioral results are consistent with potential abnormalities in frontal and supplementary eye fields in patients with SZ.

Increased saccadic rate during smooth pursuit eye movements in patients at Ultra High Risk for developing a psychosis

Abnormalities in eye tracking are consistently observed in schizophrenia patients and their relatives and have been proposed as an endophenotype of the disease. The aim of this study was to investigate the performance of patients at Ultra High Risk (UHR) for developing psychosis on a task of smooth pursuit eye movement (SPEM). Forty-six UHR patients and twenty-eight age and education matched controls were assessed with a task of SPEM and psychiatric questionnaires. Our results showed that both the corrective and non-corrective saccadic rates during pursuit were higher in the UHR group. There were however no differences in smooth pursuit gain between the two groups. The saccadic rate was related to positive UHR symptoms. Our findings indicate that abnormalities in SPEM are already present in UHR patients, prior to a first psychotic episode. These abnormalities occur only in the saccadic system.

Impaired smooth pursuit in schizophrenia results from prediction impairment only

BACKGROUND

Oculomotor abnormality is one of the endophenotypes in schizophrenia. The predictive component of smooth pursuit can be studied by comparing the gain, i.e., the ratio of smooth eye position to target position, during predictable (pure sinusoidal) and unpredictable (pseudorandom) target motions. The aim of this experiment was to study predictive and nonpredictive components of smooth pursuit in two groups of schizophrenia patients compared with control subjects.

METHODS

Fifty-one schizophrenia patients (40 nondeficit and 11 deficit) and 21 control subjects were studied. During a predictable task, subjects were asked to track a sinusoidal target (.4 Hz). For the unpredictable task, the pseudorandom target motion consisted of five superimposed sinusoidal waveforms (.1, .2, .4, .6, and .8 Hz). The smooth eye position (eye position without saccades), gain, and phase were calculated for each frequency in each participant and for both tasks.

RESULTS

The mean sinusoidal smooth eye position gain was significantly lower in patients than in control subjects with no significant difference between deficit and nondeficit patients. During the pseudorandom task, all groups had a similar gain at .4 Hz.

CONCLUSIONS

Our study reveals that patients have a normal nonpredictive component of smooth pursuit, regardless of their level of negative symptoms. In contrast, the predictive mechanisms involved in eye pursuit were impaired in schizophrenia patients. These results indicate that poor pursuit performance during smooth pursuit is primarily a consequence of a predictive problem and is not related to the ability to generate an accurate pursuit maintenance response.

Sensorimotor transformation deficits for smooth pursuit in first-episode affective psychoses and schizophrenia

BACKGROUND

Smooth pursuit deficits are an intermediate phenotype for schizophrenia that may result from disturbances in visual motion perception, sensorimotor transformation, predictive mechanisms, or alterations in basic oculomotor control. Which of these components are the primary causes of smooth pursuit impairments and whether they are impaired similarly across psychotic disorders remain to be established.

METHODS

First-episode psychotic patients with bipolar disorder (n = 34), unipolar depression (n = 24), or schizophrenia (n = 77) and matched healthy participants (n = 130) performed three smooth pursuit tasks designed to evaluate different components of pursuit tracking.

RESULTS

On ramp tasks, maintenance pursuit velocity was reduced in all three patients groups with psychotic bipolar patients exhibiting the most severe impairments. Open loop pursuit velocity was reduced in psychotic bipolar and schizophrenia patients. Motion perception during pursuit initiation, as indicated by the accuracy of saccades to moving targets, was not impaired in any patient group. Analyses in 138 participants followed for 6 weeks, during which patients were treated and psychotic symptom severity decreased, and no significant change in performance in any group was revealed.

CONCLUSIONS

Sensorimotor transformation deficits in all patient groups suggest a common alteration in frontostriatal networks that dynamically regulate gain control of pursuit responses using sensory input and feedback about performance. Predictive mechanisms appear to be sufficiently intact to compensate for this deficit across psychotic disorders. The absence of significant changes after acute treatment and symptom reduction suggests that these deficits appear to be stable over time.

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.

Diminished parietal cortex activity associated with poor motion direction discrimination performance in schizophrenia

The results of multiple investigations indicate visual motion-processing abnormalities in schizophrenia. There is little information, however, about the time course and neural correlates of motion-processing abnormalities among these subjects. For the present study, 13 schizophrenia and 13 healthy subjects performed a simple motion direction discrimination task with peripherally presented moving grating stimuli (5 or 10 deg/s). Dense-array electroencephalography data were collected simultaneously. The goal was to discern whether neural deviations associated with motion-processing abnormalities among schizophrenia patients occur early or late in the visual-processing stream. Schizophrenia patients were worse at judging the direction of motion gratings, had enhanced early neural activity (about 90 ms after stimulus onset), and deficient target detection-related late neural activity over parietal cortex (about 400 ms after stimulus onset). In addition, there was a strong association (accounting for 36% of performance variance) between poor behavioral performance and lower target detection-related brain activity among schizophrenia patients. These findings suggest that abnormalities in later stages of motion-processing mechanisms, perhaps beyond extrastriate cortex, may account for behavioral deviations among schizophrenia subjects.

From bench to bedside: translating new research from genetics and neuroimaging into treatment development for early-onset schizophrenia

OBJECTIVE

Children and adolescents with schizophrenia share a similar pattern of phenomenological, genetic and cognitive abnormalities to adults with schizophrenia. However, an early-onset of schizophrenia (EOS) (prior to 18 years of age) is associated with a higher frequency of risk indicators associated with schizophrenia (e.g. developmental delays and familial spectrum disorders) and a worse long-term outcome. This overview examines recent research on the neurobiological alterations, possible causes, developmental trajectory and treatment of EOS and attempts to identify gaps in the field.

METHOD

The authors provide a selective review of major findings from genetics, neuroimaging and treatment studies of pediatric schizophrenia that were presented at a workshop sponsored by the National Institute of Mental Health. These data are synthesized in conjunction with preclinical studies into a model of the pathophysiology of EOS.

RESULTS

EOS is associated with a high frequency of cytogenetic abnormalities (e.g. velocardiofacial syndrome, sex chromosome anomalies) and other rare denovo chromosomal aberrations. Brain imaging research in adolescents with EOS has revealed a progressive loss of cortical grey matter post-onset of psychosis and subtle abnormalities in white matter microstructure. Although EOS patients are more likely to be treatment-refractory than their adult counterparts, there are substantial data that this subgroup is particularly responsive to clozapine.

CONCLUSIONS

Genetic or environmental factors operating during adolescence that reduce frontal capacity might contribute to an EOS in susceptible individuals. Additional longitudinal studies of adolescents with schizophrenia are needed to better understand the relationship between structural changes in fronto-limbic regions, stress responsivity, and cognitive and neurochemical development.

Association analysis of COMT polymorphisms with schizophrenia and smooth pursuit eye movement abnormality

Schizophrenia is a multifactorial disorder characterized by the contribution of multiple susceptibility genes that may act in conjunction with epigenetic processes and environmental factors. The catechol-O-methyltransferase (COMT) gene, which is located in the 22q11 microdeletion, has been considered as a candidate gene for schizophrenia because of its ability to degrade catecholamines, including dopamine. In a genetic analysis, neurophysiological endophenotype in schizophrenia, such as smooth pursuit eye movement (SPEM) disturbance, is considered to be a good trait marker, because it may be under more direct genetic control. This study was performed to examine the genetic association of COMT polymorphisms with the risk of schizophrenia and SPEM abnormality in a Korean population. Six single-nucleotide polymorphisms of COMT were genotyped by TaqMan assay. Their genetic effects on the risk of schizophrenia were analyzed in 354 patients and 396 controls using chi(2) analyses. Among the schizophrenic patients, 166 subjects were selected for association analyses of COMT polymorphisms with SPEM abnormality. From the six COMT polymorphisms, rs6267 showed an association with the reduced risk of schizophrenia after correction (P(corr) = 0.02). In analysis of SPEM abnormality, no significant associations were detected with COMT polymorphisms. The results of the present study provide the evidence that in a Korean population, COMT on the 22q11 locus is likely involved in the development of schizophrenia, but not in the SPEM function abnormality.

COMT val(158)met genotype and smooth pursuit eye movements in schizophrenia

The association between the catechol-O-methyltransferase (COMT) val(158)met polymorphism (rs4680) and smooth pursuit eye movements (SPEM) was investigated in 110 schizophrenia patients and 96 controls. Patients had lower steady-state pursuit gain and made more frequent saccades than controls. Genotype was not associated with schizophrenia or SPEM, in either group or the combined sample. SPEM deficits in schizophrenia appear to be determined by genotypes other than rs4680, although the study may have lacked power to detect small effects.

Dopamine transporter polymorphism modulates oculomotor function and DAT1 mRNA expression in schizophrenia

Smooth pursuit eye movement (SPEM) deficit is an established schizophrenia endophenotype with a similar neurocognitive construct to working memory. Frontal eye field (FEF) neurons controlling SPEM maintain firing when visual sensory information is removed, and their firing rates directly correlate with SPEM velocity. We previously demonstrated a paradoxical association between a functional polymorphism of dopamine signaling (COMT gene) and SPEM. Recent evidence implicates the dopamine transporter gene (DAT1) in modulating cortical dopamine and associated neurocognitive functions. We hypothesized that DAT1 10/10 genotype, which reduces dopamine transporter expression and increases extracellular dopamine, would affect SPEM. We examined the effects of DAT1 genotype on: Clinical diagnosis in the study sample (n = 418; 190 with schizophrenia), SPEM measures in a subgroup with completed oculomotor measures (n = 200; 87 schizophrenia), and DAT1 gene expression in FEF tissue obtained from postmortem brain samples (n = 32; 16 schizophrenia). DAT1 genotype was not associated with schizophrenia. DAT1 10/10 genotype was associated with better SPEM in healthy controls, intermediate SPEM in unaffected first-degree relatives of schizophrenia subjects, and worse SPEM in schizophrenia subjects. In the gene expression study, DAT1 10/10 genotype was associated with significantly reduced DAT1 mRNA transcript in FEF tissue from healthy control donors (P < 0.05), but higher expression in schizophrenia donors. Findings suggest regulatory effects of another gene(s) or etiological factor in schizophrenia, which modulate DAT1 gene function.

Encoding dysfunctions in a dynamic-static paradigm for visuospatial working memory in first-episode psychosis patients: a 2-year follow-up study

AIM

To investigate static and dynamic visuospatial working memory (VSWM) processes in first-episode psychosis (FEP) patients and explore the validity of such measures as specific trait markers of schizophrenia.

METHODS

Twenty FEP patients and 20 age-, sex-, laterality- and education-matched controls carried out a dynamic and static VSWM paradigm. At 2-year follow up 13 patients met Diagnostic and Statistical Manual (of Mental Health Disorders)--Fourth Edition (DSM-IV) criteria for schizophrenia, 1 for bipolar disorder, 1 for brief psychotic episode and 5 for schizotypal personality disorder.

RESULTS

Compared with controls, the 20 FEP patients showed severe impairment in the dynamic VSWM condition but much less impairment in the static condition. No specific bias in stimulus selection was detected in the two tasks. Two-year follow-up evaluations suggested poorer baseline scores on the dynamic task clearly differentiated the 13 FEP patients who developed schizophrenia from the seven who did not.

CONCLUSIONS

Results suggest deficits in VSWM in FEP patients. Specific exploratory analyses further suggest that deficit in monitoring-manipulation VSWM processes, especially involved in our dynamic VSWM task, can be a reliable marker of schizophrenia.

Differential activation patterns of occipital and prefrontal cortices during motion processing: evidence from normal and schizophrenic brains

Visual motion perception is normally mediated by neural processing in the posterior cortex. Focal damage to the middle temporal area (MT), a posterior extrastriate region, induces motion perception impairment. It is unclear, however, how more broadly distributed cortical dysfunction affects this visual behavior and its neural substrates. Schizophrenia manifests itself in a variety of behavioral and perceptual abnormalities that have proved difficult to understand through a dysfunction of any single brain system. One of these perceptual abnormalities involves impaired motion perception. Motion processing provides an opportunity to clarify the roles of multiple cortical networks in both healthy and schizophrenic brains. Using fMRI, we measured cortical activation while participants performed two visual motion tasks (direction discrimination and speed discrimination) and one nonmotion task (contrast discrimination). Normal controls showed robust cortical activation (BOLD signal changes) in MT during the direction and speed discrimination tasks, documenting primary processing of sensory input in this posterior region. In patients with schizophrenia, cortical activation was significantly reduced in MT and significantly increased in the inferior convexity of the prefrontal cortex, an area that is normally involved in higher level cognitive processing. This shift in cortical responses from posterior to prefrontal regions suggests that motion perception in schizophrenia is associated with both deficient sensory processing and compensatory cognitive processing. Furthermore, this result provides evidence that in the context of broadly distributed cortical dysfunction, the usual functional specificity of the cortex becomes modified, even across the domains of sensory and cognitive processing.

Eye movement deficits in schizophrenia: investigation of a genetically homogenous Icelandic sample

BACKGROUND

Deficits in antisaccade (AS) and smooth pursuit eye movements (SPEM) are promising endophenotypes in genetic studies of schizophrenia. The Icelandic population lends itself ideally to genetic studies due to its ethnic homogeneity and well-documented genealogy. The primary aim of this study was to assess AS and SPEM performance in a large Icelandic sample. Additional aims were to investigate the relationship between AS and SPEM task performance and to assess internal consistency, within-session performance changes and effects of SPEM target velocity on performance.

METHOD

Patients with schizophrenia (N = 118) and healthy controls (N = 109) matched for age and gender underwent infrared oculographic assessment of AS and SPEM (at target velocities of 12 degrees , 24 degrees and 36 degrees /s).

RESULTS

On the AS task patients displayed significantly more reflexive errors, longer latency, increased intra-individual latency variability, and reduced amplitude gain compared to controls. On the SPEM task, patients had significantly lower velocity gain and more frequent saccades during pursuit at all velocities, but group differences in velocity gain increased with increasing target velocity. Internal consistency of performance was high for all variables in both groups (Cronbach's alpha >0.77 for AS and >0.85 for SPEM) except for AS spatial error in patients (alpha = 0.38). A moderate association was found between AS and SPEM performance. By and large, patients and controls showed similar patterns of systematic within-session performance changes.

CONCLUSIONS

Our findings confirm the existence of robust eye movement deficits in schizophrenia in a large sample. These measures may be studied as endophenotypes in future studies of potential schizophrenia risk genotypes in the genetically homogenous Icelandic population.

Stress-induced dopamine release in humans at risk of psychosis: a [11C]raclopride PET study

Drugs that increase dopamine levels in the brain can cause psychotic symptoms in healthy individuals and worsen them in schizophrenic patients. Psychological stress also increases dopamine release and is thought to play a role in susceptibility to psychotic illness. We hypothesized that healthy individuals at elevated risk of developing psychosis would show greater striatal dopamine release than controls in response to stress. Using positron emission tomography and [(11)C]raclopride, we measured changes in synaptic dopamine concentrations in 10 controls and 16 psychometric schizotypes; 9 with perceptual aberrations (PerAb, ie positive schizotypy) and 7 with physical anhedonia (PhysAn, ie negative schizotypy). [(11)C]Raclopride binding potential was measured during a psychological stress task and a sensory-motor control. All three groups showed significant increases in self-reported stress and cortisol levels between the stress and control conditions. However, only the PhysAn group showed significant stress-induced dopamine release. Dopamine release in the entire sample was significantly negatively correlated with smooth pursuit gain, an endophenotype linked to frontal lobe function. Our findings suggest the presence of abnormalities in the dopamine response to stress in negative symptom schizotypy, and provide indirect evidence of a link to frontal function.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

Sequential neural changes during motor learning in schizophrenia

Positron emission tomography (PET) was used to investigate differences in neural plasticity associated with learning a unique motor task in patients with schizophrenia and healthy volunteers. Working with a robotic manipulandum, subjects learned reaching movements in a force field. Visual cues were provided to guide the reaching movements. PET rCBF measures were acquired while participants learned the motor skill over successive runs. The groups did not differ in behavioral performance but did differ in their rCBF activity patterns. Healthy volunteers displayed blood flow increases in primary motor cortex and supplementary motor area with motor learning. The patients with schizophrenia displayed an increase in the primary visual cortex with motor learning. Changes in these regions were positively correlated with changes in each group's motor accuracy, respectively. This is the first study to employ a unique arm-reaching motor learning test to assess neural plasticity during multiple phases of motor learning in patients with schizophrenia. The patients may have an inability to rapidly tune motor cortical neural populations to a preferred direction. The visual system, however, appears to be highly compensated in schizophrenia and the inability to rapidly modulate the motor cortex may be substantially corrected by the schizophrenic group's visuomotor adaptations.

Refining the predictive pursuit endophenotype in schizophrenia

BACKGROUND

To utilize fully a schizophrenia endophenotype in gene search and subsequent neurobiological studies, it is critical that the precise underlying physiologic deficit is identified. Abnormality in smooth pursuit eye movements is one of the endophenotypes of schizophrenia. The precise nature of the abnormality is unknown. Previous work has shown a reduced predictive pursuit response to a briefly masked (i.e., invisible) moving object in schizophrenia. However, the overt awareness of target removal can confound the measurement.

METHODS

This study employed a novel method that covertly stabilized the moving target image onto the fovea. The foveal stabilization was implemented after the target on a monitor had oscillated at least for one cycle and near the change of direction when the eye velocity momentarily reached zero. Thus, the subsequent pursuit eye movements were completely predictive and internally driven. Eye velocity during this foveally stabilized smooth pursuit was compared among schizophrenia patients (n = 45), their unaffected first-degree relatives (n = 42), and healthy comparison subjects (n = 22).

RESULTS

Schizophrenia patients and their unaffected relatives performed similarly and both had substantially reduced predictive pursuit acceleration and velocity under the foveally stabilized condition.

CONCLUSIONS

These findings show that inability to maintain internal representation of the target motion or integration of such information into a predictive response may be the specific brain deficit indexed by the smooth pursuit endophenotype in schizophrenia. Similar performance between patients and unaffected relatives suggests that the refined predictive pursuit measure may index a less complex genetic origin of the eye-tracking deficits in schizophrenia families.

Neurophysiological biomarkers for drug development in schizophrenia

Schizophrenia represents a pervasive deficit in brain function, leading to hallucinations and delusions, social withdrawal and a decline in cognitive performance. As the underlying genetic and neuronal abnormalities in schizophrenia are largely unknown, it is challenging to measure the severity of its symptoms objectively, or to design and evaluate psychotherapeutic interventions. Recent advances in neurophysiological techniques provide new opportunities to measure abnormal brain functions in patients with schizophrenia and to compare these with drug-induced alterations. Moreover, many of these neurophysiological processes are phylogenetically conserved and can be modelled in preclinical studies, offering unique opportunities for use as translational biomarkers in schizophrenia drug discovery.

Schizophrenia endophenotypes as treatment targets

Schizophrenia is a complex disorder that encompasses several clinical symptom domains and functional impairments. Existing treatments are meager, effective only against positive symptoms without benefiting negative symptoms and functional impairments. The drug discovery process has focused mostly on targeting D2 dopamine receptors. This followed the serendipitous discovery of the antipsychotic effects of chlorpromazine in the 1950s and, more recently, clozapine. There is a need to identify novel mechanisms in order to discover novel drugs that are effective against each of the symptom clusters and functional impairments associated with the illness. Neurophysiological studies in schizophrenia over the past 3 decades have identified several brain deficits that are stable, using valid animal models that are related to the etiology of the disorder. Many of these deficits are distinct and heritable; these are called endophenotypes. Many have well-characterized neurobiology and may therefore provide molecular targets for drug development. In addition, these endophenotypes help reduce the heterogeneity by identifying homogeneous subgroups of patients with similar pathophysiology, symptoms and functional deficits. Clinical trials of drugs, whose development is based on an endophenotype, will have enhanced statistical power when the trial is carried out in an appropriate cohort of subjects using outcome measures related to the corresponding endophenotype. Furthermore, genes that are associated with these endophenotypes are beginning to be identified. These findings will identify novel molecular targets for drug development with treatment implications for clinical symptom complex and functional deficits marked by the endophenotype. As endophenotypes are present during childhood and adolescence, novel drugs that are developed on the basis of this subgroup could have implications for preventive strategies in schizophrenia.

Low frequency rTMS over posterior parietal cortex impairs smooth pursuit eye tracking

The role of the posterior parietal cortex in smooth pursuit eye movements remains unclear. We used low frequency repetitive transcranial magnetic stimulation (rTMS) to study the cognitive and neural systems involved in the control of smooth pursuit eye movements. Eighteen participants were tested on two separate occasions. On each occasion we measured smooth pursuit eye tracking before and after 6 min of 1 Hz rTMS delivered at 90% of motor threshold. Low frequency rTMS over the posterior parietal cortex led to a significant reduction in smooth pursuit velocity gain, whereas rTMS over the motor cortex had no effect on gain. We conclude that low frequency offline rTMS is a potentially useful tool with which to explore the cortical systems involved in oculomotor control.