Impaired eye tracking in undergraduates with schizotypal personality disorder

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.

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: neurodevelopmental and psychosocial trajectories

Schizotypal personality research holds the promise of critically important insights into the etiology and ultimate prevention of schizophrenia. This article provides a critical overview of diagnostic, developmental, demographic, psychosocial, genetic, neurodevelopmental, psychophysiological, neurochemical, neurocognitive, brain imaging, and prevention-treatment issues pertaining to this personality disorder. It is argued that genetic and early environmental influences act in concert to alter brain structure/function throughout development, resulting in disturbances to basic cognitive and affective processes that give rise to three building blocks of schizotypy-cognitive-perceptual, interpersonal, and disorganized features. Two clinical subtypes are hypothesized: (a) neurodevelopmental schizotypy, which has its roots in genetic, prenatal, and early postnatal factors, is relatively stable, has genetic affinity to schizophrenia, and may benefit preferentially from pharmacological intervention, and (b) pseudoschizotypy, which is unrelated to schizophrenia, has its roots in psychosocial adversity, shows greater symptom fluctuations, and may be more responsive to psychosocial intervention.

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

Individuals with schizotypal personality disorder or high scores in questionnaires measuring schizotypy are at high risk for the development of schizophrenia and they also share some of the same phenotypic characteristics such as eye-tracking dysfunction (ETD). The question arises whether these individuals form a distinct high-risk group in the general population or whether schizotypy and ETD co-vary in the general population with no distinct cutoff point for a high-risk group. A large sample of military conscripts aged 18-25 were screened using oculomotor, cognitive and psychometric tools for the purposes of a prospective study on predisposing factors for the development of psychosis. Schizotypy measured using the perceptual aberration scale (PAS) and the schizotypal personality questionnaire (SPQ), anxiety and depression, measured using the Symptom Checklist 90-R, had no effect on pursuit performance in the total sample. Small groups of individuals with very high scores in schizotypy questionnaires were then identified. These groups were not mutually exclusive. The high PAS group had higher root-mean-square error scores (a quantitative measure for pursuit quality) than the total sample, and the high disorganized factor of SPQ group had lower gain and higher saccade frequencies in pursuit than the total sample. The presence of significant differences in pursuit performance only for predefined high schizotypy groups favors the hypothesis that individuals with high schizotypy might present one or more high-risk groups, distinct from the general population, that are prone to ETD as that observed in schizophrenia.

Antisaccade and smooth pursuit performance in positive- and negative-symptom schizotypy

Schizophrenic patients have well-documented abnormalities in smooth pursuit eye movements and antisaccade performance. In populations at risk for schizophrenia, smooth pursuit abnormalities are also well documented. Antisaccade deficits have been replicated in high-risk populations as well, but the findings are more variable and the reasons for the variability are not clear. Some evidence suggests that antisaccade deficits increase in high-risk populations in relation to the presence of positive symptoms. Whether antisaccade deficits increase in relation to negative symptoms in high-risk populations is relatively uninvestigated. We evaluated antisaccade and pursuit performance in "psychometric schizotypes" who had elevated scores on either the Perceptual Aberration Scale (PerAb; i.e., positive symptoms) or the Physical Anhedonia Scale (PhysAnh; i.e., negative symptoms) but not both, and in normal controls. We used the standard version of the antisaccade task, for which results in positive-symptom schizotypes have previously been reported, and investigated performance on a gap and overlap version. We replicated the finding that a significantly larger percentage of positive-symptom schizotypes than controls have elevated antisaccade error rates on the standard antisaccade task (P=0.03); the percentage of negative-symptom schizotypes with elevated antisaccade error rates did not differ from that of control subjects. Neither schizotypal group was impaired on the gap or overlap versions of the task. On the pursuit task, a higher percentage of positive- and negative-symptom schizotypes were classified as having deviant performance than control subjects (both Ps<0.04). These findings suggest that antisaccade deficits may be better at identifying high-risk subjects with positive symptoms. Pursuit deficits identified both positive- and negative-symptom schizotypes, but was better at identifying the latter.

Cognitive and brain function in schizotypal personality disorder

Schizotypal personality disorder, a diagnosis defined partially in terms of a genetic relatedness to schizophrenia, has begun to receive extensive investigative study. While the exact etiologic relationship between schizotypal personality disorder and schizophrenia remains to be determined, three models have been considered: (1) the two may be distinct disorders, (2) they may be essentially identical disorders but expressed with different degrees of severity, or (3) they may be related disorders with a partially overlapping etiology that might account for the many similarities yet the lack of psychosis or severe deficits in schizotypal individuals. Some of the recent research in the structural and functional neuroanatomy, neurochemistry, cognitive function, and pharmacology of schizotypal personality disorder is reviewed with citation of the most recent findings from our laboratory and others. Both schizotypal and schizophrenic subjects appear to show abnormalities in temporal lobe volume, but schizotypal subjects do not appear to show the volumetric decreases in frontal cortex that schizophrenic patients evidence. Abnormalities in thalamic nuclei parallel these findings-the pulvinar, which projects to temporal association and sensory cortices, is reduced in both disorders, but the mediodorsal nucleus, which projects extensively to the frontal cortex, is reduced in schizophrenic patients but not in schizotypal patients. Functional imaging studies suggest that there may be abnormalities in frontal activation in both disorders, but that schizotypal individuals can recruit alternative regions to accomplish tasks requiring frontal lobe activation that may help compensate. Imaging studies of the subcortex including FDG/PET imaging of metabolic activity during a verbal learning task, SPECT imaging studies which measure binding of IBZM and its displacement following amphetamine administration, and plasma HVA determinations following 2-deoxyglucose administration all suggest the possibility of relatively reduced dopaminergic subcortical activity in schizotypal individuals compared to schizophrenic patients. Cognitive function is also impaired in the areas of working memory, verbal learning, and attention in schizotypal patients, as in schizophrenic patients, and they may be particularly susceptible to cognitive tasks with high context dependence, as in schizophrenia. Preliminary trials of catecholaminergic agents suggest that these agents may be able to improve these impaired cognitive functions.

Eye movement dysfunction as a biological marker of risk for schizophrenia

OBJECTIVE

Our aim was to review smooth pursuit eye movement (SPEM) studies in schizophrenia and groups at high risk for schizophrenia, with a view to evaluating the utility of SPEM dysfunction as a biological marker of risk for schizophrenia.

METHOD

Smooth pursuit eye movement studies, related saccade function and the unresolved issues in this area of schizophrenia research were addressed. The different perspectives on the trait marker status of SPEM dysfunction, provided by both high-risk studies and related developmental research were considered. Attention was also given to the relationship between eye movement dysfunction and symptom profiles.

RESULTS

Converging evidence points to the robust and specific nature of SPEM dysfunction in schizophrenia, and highlights the role of frontal lobe and a related network dysfunction. The vast majority of 'high risk' studies support the view that SPEM dysfunction is also genetically specific to schizophrenia, and is not simply due to the overt expression of this illness. Studies assessing SPEM in relation to symptomatology show an association with the Disorganisation syndrome in particular.

CONCLUSIONS

Evidence for the specificity of SPEM dysfunction to diagnosed schizophrenia, as well as to healthy individuals with a genetic vulnerability to schizophrenia, suggests that the SPEM task has efficacy as a test of gene carrier status in schizophrenia, and therefore as a trait marker of risk for schizophrenia. Future studies should seek to explore the relationships between SPEM and other eye movement dysfunctions (antisaccades, express saccades), in view of evidence that some of these dysfunctions also show specificity for schizophrenia.

The gap effect in pro-saccades and anti-saccades in psychometric schizotypes

Schizophrenic patients and their first-degree relatives exhibit deficits in the anti-saccade task. In the present study, anti-saccade task performance was examined in subjects with 'high' and 'low' expressions of the schizotypal personality trait. For that purpose, the SPQ-G, the German adaptation of the Schizotypal Personality Questionnaire (SPQ; Raine, 1991), was filled in by 489 university students. Twenty and 21 participants with 'high' and 'low' SPQ-G scores, respectively, were compared with respect to saccadic eye movements elicited under the overlap and 200 ms gap conditions of the pro- and anti-saccade tasks. Each task block comprised 150 trials, 75 to either side in random order. The order of presentation of the task blocks was counterbalanced across the participants of each group. Saccadic reaction times were slower during the anti- as compared to the pro-saccade task and under the overlap as compared to the gap condition. Direction errors occurred almost exclusively during the anti-saccade task, express saccades mainly under the pro-saccadic gap condition. High-schizotypal participants did not differ significantly from low-schizotypal participants in any of these measures. While these results might suggest normal anti-saccade task performance in schizotypal personality as defined by the SPQ-G, the sampling strategy adopted in the present study is the more plausible explanation for the lack of group differences.

Smooth pursuit eye tracking and visual fixation in psychosis-prone individuals

Subjects identified by Perceptual Aberration-Magical Ideation (Per-Mag) scores (n=97), Social Anhedonia (SocAnh) scores (n=45), and Physical Anhedonia (PhysAnh) scores (n=31) as well as normal controls (n=94), underwent psychophysiological and clinical assessment. This is the first published investigation of pursuit system functioning in three groups of questionnaire-identified at-risk individuals. Pursuit during a simple non-monitor tracking task was measured using root-mean-square error (RMSE) scores and pursuit gain scores. Fixation performance was measured in terms of number of saccades away from the central fixation point. The at-risk subjects were more likely to display aberrant smooth pursuit tracking than controls, though there were no significant differences between the at-risk subjects endorsing items relevant to positive-symptom schizotypy and those endorsing items pertaining to negative-symptom schizotypy. The groups did not differ significantly in their visual fixation performance. Participants were also evaluated for the presence of Axis I symptomatology and psychotic-like experiences. Neither the experimental subjects nor the control subjects displayed a significant association between ocular motor performance and psychotic-like experiences. These findings are consistent with prior evidence that pursuit tracking is a trait characteristic, independent of clinical status.

Eye tracking in normals: spem asymmetries and association with schizotypy

SPEM was recorded electro-oculographically during visual tracking of sinusoidal targets oscillating at .4 and .8 cycles per second in one hundred nineteen undergraduates. The logarithms of median root mean square values were used to assess tracking accuracy for leftward and rightward halfcycles of tracking. Over the entire sample, there was a significant superiority of rightward over leftward tracking, which, given evidence for the ipsilateral mediation of SPEM at the cortical level, suggests a right hemisphere predominance in the control of SPEM in normal subjects. Individual tracking asymmetry was associated with overall tracking accuracy such that subjects with relatively deficient leftward tracking and those with a larger absolute magnitude of asymmetry had poorer overall tracking. High scores on an MMPI schizotypy measure (Sum 2-7-8-0) were significantly related to poorer overall SPEM accuracy, individual tracking asymmetry, the absolute magnitude of tracking asymmetry, and phase lag, though the subjects' sex, handedness, and crossed hand-foot dominance were found to affect the relationships between schizotypy and tracking accuracy. These findings suggest that although control of SPEM may be predominantly right hemispheric, in some persons with a vulnerability to schizophrenia spectrum disorders, expressed as poorer overall SPEM accuracy and high schizotypy scores, left hemisphere-mediated (leftward) SPEM may be particularly impaired.

Comparison of schizotypal relatives of schizophrenic versus affective probands

In order to investigate possible heterogeneity in schizotypal personality disorder (SPD), two groups of schizotypals, one related to schizophrenic probands (FSPD) (n = 34) and one related to affective disorder probands (NFSPD) (n = 14), ascertained in the same family study, were compared. The FSPD group had more inadequate rapport; the groups did not differ in the frequency of any other symptoms of SPD. NFSPDs had higher rates of comorbid histrionic PD and a trend for higher rates of impulsive/dramatic cluster PDs. FSPDs had a trend for higher rates of anxiety disorders. There was a higher risk of bipolar disorder in the relatives of NFSPDs and higher risk for anxiety disorders in the relatives of FSPDs. The relatives of NFSPDs had higher rates for histrionic, narcissistic, and atypical PDs and for having at least one PD.