Relationship between smooth pursuit eye-tracking and cognitive performance in schizophrenia

Amphetamine-induced alteration to gaze parameters: A novel conceptual pathway and implications for naturalistic behavior

Amphetamine produces a multiplicity of well-documented end-order biochemical, pharmacological and biobehavioural effects. Mechanistically, amphetamine downregulates presynaptic and postsynaptic striatal monoamine (primarily dopaminergic) systems, producing alterations to key brain regions which manifest as stereotyped ridged behaviour which occurs under both acute and chronic dosing schedules and persists beyond detoxification. Despite evidence of amphetamine-induced visual attentional dysfunction, no conceptual synthesis has yet captured how characteristic pharmaco-behavioural processes are critically implicated via these pathways, nor described the potential implications for safety-sensitive behaviours. Drawing on known pathomechanisms, we propose a cross-disciplinary, novel conceptual functional system framework for delineating the biobehavioural consequences of amphetamine use on visual attentional capacity and discuss the implications for functional and behavioural outcomes. Specifically, we highlight the manifest implications for behaviours that are conceptually driven and highly dependent on visual information processing for timely execution of visually-guided movements. Following this, we highlight the potential impact on safety-sensitive, but common behaviours, such as driving a motor vehicle. The close pathophysiological relationship between oculomotor control and higher-order cognitive processes further suggests that dynamic measurement of movement related to the motion of the eye (gaze behaviour) may be a simple, effective and direct measure of behavioural performance capabilities in naturalistic settings. Consequently, we discuss the potential efficacy of ocular monitoring for the detection and monitoring of driver states for this drug user group, and potential wider application. Significance statement: We propose a novel biochemical-physiological-behavioural pathway which delineates how amphetamine use critically alters oculomotor function, visual-attentional performance and information processing capabilities. Given the manifest implications for behaviours that are conceptually driven and highly dependent on these processes, we recommend oculography as a novel means of detecting and monitoring gaze behaviours during naturalistic tasks such as driving. Real-word examination of gaze behaviour therefore present as an effective means to detect driver impairment and prevent performance degradation due to these drugs.

Eye movements and neurocognitive function in treatment resistant schizophrenia: a pilot study

Objectives: It is increasingly important to develop predictors of treatment response and outcome in schizophrenia. Neuropsychological impairments, particularly those reflecting frontal lobe function, appear to predict poor outcome. Eye movement abnormalities probably also reflect frontal lobe deficits. We wished to see if these two aspects of schizophrenia were correlated and whether they could distinguish a treatment resistant from a treatment responsive group.

Methods: Ten treatment resistant schizophrenic patients were compared with ten treatment responsive patients on three eye movement paradigms (reflexive saccades, antisaccades and smooth pursuit), clinical psychopathology (BPRS, SANS and CGI) and a neuropsychological test battery designed to detect frontal lobe dysfunction. Ten aged-matched controls also carried out the eye movement tasks.

Results: Both treatment responsive (p = 0.038) and treatment resistant (p = 0.007) patients differed significantly from controls on the antisaccade task. The treatment resistant group had a higher error rate than the treatment responsive group, but the difference was not statistically significant. Similar poor neuropsychological test performance was found in both groups.

Conclusions: To demonstrate the biological differences characteristic of treatment resistance, larger sample sizes and wider differences in outcome between the two groups are necessary.

Predictive pursuit association with deficits in working memory in psychosis

BACKGROUND

Deficits in smooth pursuit eye movements are an established phenotype for schizophrenia (SZ) and are being investigated as a potential liability marker for bipolar disorder. Although the molecular determinants of this deficit are still unclear, research has verified deficits in predictive pursuit mechanisms in SZ. Because predictive pursuit might depend on the working memory system, we have hypothesized a relationship between the two in healthy control subjects (HC) and SZ and here examine whether it extends to psychotic bipolar disorder (BDP).

METHODS

Volunteers with SZ (n = 38), BDP (n = 31), and HC (n = 32) performed a novel eye movement task to assess predictive pursuit as well as a standard visuospatial measure of working memory.

RESULTS

Individuals with SZ and BDP both showed reduced predictive pursuit gain compared with HC (p < .05). Moreover, each patient group showed worse performance in visuospatial working memory compared with control subjects (p < .05). A strong correlation (r = .53, p = .007) was found between predictive pursuit gain and working memory in HC, a relationship that showed a trend correlation within the BDP group but not among SZ.

CONCLUSIONS

Individuals with SZ and BDP showed similar deficits in predictive pursuit, suggesting that this alteration could be a characteristic trait of the psychosis domain. The correlation between predictive pursuit and working memory in HC supports the assumption that working memory is related to predictive pursuit eye movements; however, the degradation of working memory in people with psychosis disrupts its association with eye-tracking behavior.

Comparison of putative intermediate phenotypes in schizophrenia patients with and without obsessive-compulsive disorder: examining evidence for the schizo-obsessive subtype

Obsessive-compulsive symptoms or obsessive-compulsive disorder (OCD) is estimated to occur in up to 30% of patients with schizophrenia. Whether this subgroup of patients is cognitively, affectively, or physiologically distinct remains unclear. 204 schizophrenia patients, 15 who also met criteria for a diagnosis of OCD, and 147 healthy controls were examined on several intermediate phenotypes. The patient groups did not differ from each other except that the co-morbid group exhibited an elevated rate of eye-tracking dysfunction. Results suggest that OCD-co-morbid patients did not comprise a distinct subgroup based on the measures studied here, although systematic assessment of larger cohorts is warranted.

Neuropsychological correlates of eye movement abnormalities in schizophrenic patients and their unaffected relatives

Impairments on neuropsychological and eye movement tasks have been demonstrated in schizophrenic patients and also reported in their unaffected relatives. However, it is not clear to what extent these phenotypes overlap. This study examined the relationship between specific eye movement and neuropsychological measures. The relationship between performance on eye movement and neuropsychological tasks was measured in 79 schizophrenic patients (63% from multiply affected families), 129 of their healthy first-degree relatives, and 72 normal controls. Antisaccade scores were correlated with most measures of neurocognitive functioning, and this correlation was strongest in schizophrenic patients in all cases. In the schizophrenic patients, but not their relatives or controls, the antisaccade distractibility error (ADE) score correlated significantly with current intelligence, verbal memory (immediate and delayed recall), and associative learning. In the case of crystallised IQ and delayed verbal memory, smaller correlations were present in unaffected relatives, although neither survived Bonferroni correction. Smooth pursuit performance was unrelated to any neuropsychological measure. Our study suggests that antisaccade errors are likely to represent part of a generalized neuropsychological deficit in schizophrenia.

Working memory in schizophrenia: a meta-analysis

BACKGROUND

Memory impairment is being recognized increasingly as an important feature of the neuropsychology of schizophrenia. Dysfunction of working memory, a system for the short-term storage and manipulation of information, may relate to a number of core symptoms of schizophrenia. Many studies have examined working memory function in schizophrenia but a clear understanding of the nature and extent of any deficit has been elusive.

METHOD

A systematic review and meta-analysis of studies comparing working memory function in subjects with schizophrenia and healthy controls was performed. Following a comprehensive literature search, meta-analyses were conducted on 36 measures of phonological, visuospatial and central executive working memory functioning, encompassing 441 separate results from 187 different studies.

RESULTS

Statistically significant effect sizes were found for all working memory measures, indicating deficits in schizophrenia groups. Some of these were robust findings in the absence of evidence of significant heterogeneity or publication bias. Meta-regression analyses showed that the working memory deficit was not simply explained by discrepancies in current IQ between schizophrenia and control groups.

CONCLUSIONS

Large deficits in working memory were demonstrated in schizophrenia groups across all three working memory domains. There were, however, no clear differences across subdomains or between particular working memory tasks. There was substantial heterogeneity across results that could only be partly explained.

Smooth pursuit in schizophrenia: a meta-analytic review of research since 1993

Abnormal smooth pursuit eye-tracking is one of the most replicated deficits in the psychophysiological literature in schizophrenia [Levy, D. L., Holzman, P. S., Matthysse, S., & Mendell, N. R. (1993). Eye tracking dysfunction and schizophrenia: A critical perspective. Schizophrenia Bulletin, 19, 461-505]. We used meta-analytic procedures to quantify patient-control differences in eye-tracking and to evaluate potential moderators of effect size including patient and target characteristics and characteristics of the control population (matched or not). The magnitude of patient-control differences in pursuit depended on the measure. Global measures had large effect sizes. Among specific measures, maintenance gain and leading saccades yielded large effect sizes, with gain also yielding the narrowest confidence interval. Effect sizes associated with specific measures of smooth pursuit vs. specific measures of intrusive saccades did not clearly implicate one system over the other. Patient demographics and target characteristics generally had little influence on effect sizes. However, studies that failed to sex-match patients and controls tended to have smaller effect sizes for maintenance gain and catch-up saccade rate. Average effect sizes and confidence limits for global measures of pursuit and for maintenance gain place these measures alongside the very strongest neurocognitive measures in the literature [Heinrichs, R. W. (2004). Meta-analysis, and the science of schizophrenia: Variant evidence or evidence of variants? Neuroscience and Biobehavioral Reviews, 28, 379-394] for distinguishing between patients with schizophrenia and controls.

FAS and CFL forms of verbal fluency differ in difficulty: a meta-analytic study

The Controlled Oral Word Association (COWA) Test is a brief and sensitive measure of executive cognitive dysfunction. There are two commonly used forms of the test, one using the letters F, A, and S, and the other using C, F, and L. This study examines the relative difficulty of the two forms using a meta-analytic approach that includes multiple samples of normal individuals. The effects of age, education, gender composition, exclusion criteria, and age of study are also examined. Results indicate that the CFL form of the test is more difficult and that age, education, and the use of strict exclusion criteria influence performance. Performance is more variable for the FAS form, and age and age of study influence performance variability.

Disruption of smooth pursuit eye movements in cirrhosis: relationship to hepatic encephalopathy and its treatment

Smooth pursuit eye movements (SPEM) are the conjugate movements used to track the smooth trajectory of small dots. Jerky or 'saccadic' ocular pursuit has been reported in patients with cirrhosis, but no formal assessment of SPEM has ever been undertaken. The aim of this study was to evaluate SPEM in patients with cirrhosis and varying degrees of hepatic encephalopathy. The patient population comprised 56 individuals (31 men, 25 women) of mean age 51.1 (range, 25-70) years, with biopsy-proven cirrhosis, classified, using clinical, electroencephalographic, and psychometric variables, as either neuropsychiatrically unimpaired or as having minimal or overt hepatic encephalopathy; patients were further categorized in relation to their treatment status. The reference population comprised 28 healthy volunteers (12 men, 16 women) of mean age 47.3 (range, 26-65) years. SPEM was assessed using an electro-oculographic technique. Visual inspection of the SPEM recordings showed clear disruption of smooth pursuit in the patients with minimal hepatic encephalopathy, and more pronounced disruption, if not complete loss, of smooth pursuit in patients with overt hepatic encephalopathy. The differences observed in quantifiable SPEM indices between the healthy volunteers/unimpaired patients and those with overt hepatic encephalopathy were significant (P < .05). In conclusion, SPEM performance is impaired in patients with hepatic encephalopathy in parallel with the degree of neuropsychiatric disturbance: the pathophysiology of these changes is unknown, but retinal, extrapyramidal, and attentional abnormalities are likely to play a role. Treatment status confounds the classification of neuropsychiatric status and should be taken into account when categorizing these patients.

Cognitive dysfunctions in medicated and unmedicated patients with recent-onset schizophrenia

Schizophrenia is associated with impairments in many cognitive domains on which the influence of antipsychotics, whether conventional or atypical, remains unclear. We conducted a study of recent-onset schizophrenic patients (DSM IV) that included unmedicated (n=19), and medicated (n=19) patients matched for age and IQ. Both groups of patients had comparably low extra-pyramidal symptoms (EPS). Cognitive tasks included attentional tasks (alertness and divided attention tests), a working memory task (a verbal n-back test) and the Wisconsin Card Sorting Test (WCST). After adjustment for the Total PANSS score, we found no significant difference between the two groups of patients in any of the cognitive tasks. When compared to a group of healthy controls (n=20) matched for IQ level, unmedicated patients performed significantly worse in all cognitive tasks, with significantly longer reaction times for alertness, divided attention and working memory. These results confirm the presence of cognitive impairments in attentional and executive functions in recent-onset patients whether or not they are medicated. There was no evidence that either conventional or atypical antipsychotics had an influence on patients when EPS were excluded. Altogether, our results further support the idea that cognitive deficits in schizophrenia are enduring features per se and cannot be considered as secondary to psychiatric symptoms or to the adverse effects of medication. In addition our results suggest that antipsychotics do not have a major effect on these impairments.

Sustained activation of the hippocampus in response to fearful faces in schizophrenia

BACKGROUND

In healthy individuals, the activity of the medial temporal lobe habituates rapidly with the repeated presentation of a stimulus. Using functional magnetic resonance imaging (fMRI), we tested the hypothesis that habituation of the medial temporal lobe is reduced in schizophrenia.

METHODS

During fMRI scanning, fearful and happy faces were presented repeatedly to healthy control subjects (n =16) and patients with schizophrenia (n =18). Habituation of medial temporal lobe structures was measured by comparing the hemodynamic response occurring during the early and late portions of the presentation of each face.

RESULTS

Control subjects demonstrated significant medial temporal lobe habituation to fearful but not to happy faces. In contrast, patients with schizophrenia did not demonstrate medial temporal lobe habituation in response to fearful or happy faces. In a direct, between-group comparison, right hippocampal habituation to fearful faces was significantly greater in control subjects than in the schizophrenia patients. Also, there were no significant differences between the patients and control subjects in the early medial temporal lobe response to fearful faces, suggesting that attenuated hippocampal habituation in schizophrenia is not associated with a reduction in initial activation.

CONCLUSIONS

These findings suggest that there is abnormal modulation of hippocampal responses to fearful faces in schizophrenia.

Do schizophrenia patients make more perseverative than non-perseverative errors on the Wisconsin Card Sorting Test? A meta-analytic study

The Wisconsin Card Sorting Test (WCST) is widely used to explore executive functions in patients with schizophrenia. Among other findings, a higher number of perseverative errors has been suggested to implicate a deficit in task switching and inhibitory functions in schizophrenia. Many studies of patients with schizophrenia have focused on perseverative errors as the primary performance index in the WCST. However, do schizophrenia patients characteristically make more perseverative than non-perseverative errors compared with healthy controls? We reviewed the literature where schizophrenia patients were engaged in the WCST irrespective of the primary goal of the study. The results showed that while both schizophrenia patients and healthy participants made more perseverative than non-perseverative errors, the contrast between perseverative and non-perseverative errors is higher in schizophrenia patients only at a marginal level of significance. This result suggests that schizophrenia patients do make a comparable number of non-perseverative errors and cautions against simplistic interpretation of poor performance of schizophrenia patients in WCST as entirely resulting from impairment in set-shifting or inhibitory functions.

The relationship between antisaccades, smooth pursuit, and executive dysfunction in first-episode schizophrenia

BACKGROUND

Both oculomotor and neuropsychologic deficits have been used to support the hypothesis that schizophrenia is associated with prefrontal cortex dysfunction, but studies that have specifically investigated the relationships between these deficits have produced inconsistent findings.

METHODS

We measured both smooth pursuit and antisaccade performance in a large group (n = 109) of patients with first-episode schizophrenia and a group of matched control subjects (n = 59) and investigated the relationship between performance on these tasks and performance on a range of executive tasks. We additionally explored the relationship between these variables and measures of psychopathology at presentation and duration of untreated psychosis.

RESULTS

Antisaccade errors were significantly correlated with spatial working memory performance. Smooth pursuit gain did not correlate with any neuropsychologic measure. There were no reliable correlations between either oculomotor variables and measures of psychopathology and duration of untreated psychosis.

CONCLUSIONS

These findings suggest that in schizophrenia working memory and antisaccade performance reflect the same abnormal prefrontal substrates and that smooth pursuit is mediated by a separate neural abnormality.

Meta-analysis and the science of schizophrenia: variant evidence or evidence of variants?

Quantification (meta-analysis) of the neuroscience evidence on schizophrenia shows very modest average differences between patient and control distributions across a great variety of measures and literatures. The strongest findings involve cognitive and psychophysiological measures. Several possible explanations for this situation are reviewed including technical immaturity, methodological variability, dimensional and multiple illness models and the nature of cognitive measurement. An argument is developed that biological subtypes and endophenotypes within the broad diagnostic category of schizophrenia underpin the meta-analytic evidence. Considerations in the use of this evidence to identify illness variants are described and four candidate subtypes are proposed. Schizophrenia is a disease that will resist biological definition until its variants are isolated and extracted from the generic patient population.

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.

Distinguishing schizophrenic patients from healthy controls by quantitative measurement of eye movement parameters

BACKGROUND

Eye tracking dysfunction is a putative trait marker for susceptibility to schizophrenia; however, it cannot be recommended as an additional tool for the diagnosis of schizophrenia, due to low sensitivity and specificity.

METHODS

To assess the diagnostic potentials of combinations of eye movement paradigms, four smooth pursuit experiments (1: constant velocity of 15 degrees/sec; 2 and 3: combination with either visual or auditory distractors; 4: constant velocity of 30 degrees/sec) and two saccadic eye movement experiments (1: reflexive saccades; 2: voluntary saccades) were conducted. Fourteen patients with residual schizophrenia and 17 healthy controls were studied. Two sets of discriminant analyses (each with the resubstitution and with the "leaving one out" method) were calculated.

RESULTS

In the first set, all 10 characteristic variables were included, whereas for the second set, the three most powerful parameters were selected (two from smooth pursuit tasks and one from a voluntary saccade experiment). This procedure provided the best classification results, regarding concordance between clinical diagnoses and eye movement dysfunction (kappa = .67-.80).

CONCLUSIONS

Schizophrenic patients of the residual subtype can be differentiated from healthy individuals with considerable criterion validity on the basis of paradigms from two different ocular motor systems.

Relationships between neuropsychological and oculomotor measures in schizophrenia patients and normal controls

Establishing the relationship between oculomotor and neuropsychological impairments might facilitate a more coherent description of schizophrenia-associated neurocognitive deficits. Therefore, we assessed several aspects of neuropsychological and oculomotor function in 25 medicated schizophrenia patients and 24 age-matched controls. Neuropsychological tasks included the Wisconsin Cart Sort Test (WCST), the Trail Making Test (TMT), the Rey Auditory Verbal Learning Test, and finger tapping speed. Oculomotor functions assessed included smooth pursuit, initiation of smooth pursuit, predictive pursuit, fixation, visually guided saccades, remembered saccades, and antisaccades. Among the schizophrenia patients, predictive pursuit performance correlated significantly with finger tapping (dominant hand), TMT (both parts), and one WCST measure (categories completed). The only other significant correlation among the schizophrenia patients was between antisaccade performance and part A of the TMT. Perseverative errors during the WCST and antisaccade performance were the only measures significantly correlated among the normals. Closely related neurocognitive deficits may be responsible for impairments in TMT, WCST, predictive pursuit, and antisaccade performance in schizophrenia.

Eye movements and psychopathology in schizophrenia and bipolar disorder

The aim of this study was to examine multivariate patterns of relationships between oculomotor performance, psychopathology, and neuropsychology. Performance on smooth pursuit and saccadic eye movement tasks was assessed in three DSM-III-R diagnosis-based groups of subjects; normal (N = 55), schizophrenic (N = 29), and bipolar disorder (N = 26) and analyzed in relation to age, gender, scale for the Assessment of Negative Symptoms, Scale for the Assessment of Positive Symptoms, and Brief Psychiatric Rating Scale scores, Shipley intelligence quotient, and Wisconsin Card Sorting Test Performance. The greatest difference was a higher proportion of errors in the antisaccade task in the schizophrenic and bipolar groups, which was related to worse Wisconsin Card Sorting Test performance and was not accounted for by gender, age, education, or intelligence quotient. A significant gender and bipolar interaction showed bipolar women to have worse antisaccade performance. Abnormal smooth pursuit was more specific to schizophrenia. Antisaccade task and sine wave root-mean-square error were correlated in bipolar but not schizophrenic subjects. Scale for the Assessment of Negative Symptoms and Scale for the Assessment of Positive Symptoms scores had independent associations with the antisaccade task. Faster reaction times in the schizophrenic group to antisaccade errors were observed, suggesting an abnormality in visual attention processing and perhaps sensory gating functions. These results confirm abnormal smooth pursuit in schizophrenia and suggests that impairments in saccadic function are less specific to diagnostic group. Oculomotor performance and psychopathology seem related in complex ways to age, gender, intelligence quotient, and executive neuropsychological and possibly visual attention functions.