Lithium effect on smooth pursuit eye movements of healthy volunteers

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.

Genetics and intermediate phenotypes of the schizophrenia--bipolar disorder boundary

Categorization of psychotic illnesses into schizophrenic and affective psychoses remains an ongoing controversy. Although Kraepelinian subtyping of psychosis was historically beneficial, modern genetic and neurophysiological studies do not support dichotomous conceptualization of psychosis. Evidence suggests that schizophrenia and bipolar disorder rather present a clinical continuum with partially overlapping symptom dimensions, neurophysiology, genetics and treatment responses. Recent large scale genetic studies have produced inconsistent findings and exposed an urgent need for re-thinking phenomenology-based approach in psychiatric research. Epidemiological, linkage and molecular genetic studies, as well as studies in intermediate phenotypes (neurocognitive, neurophysiological and anatomical imaging) in schizophrenia and bipolar disorders are reviewed in order to support a dimensional conceptualization of psychosis. Overlapping and unique genetic and intermediate phenotypic signatures of the two psychoses are comprehensively recapitulated. Alternative strategies which may be implicated into genetic research are discussed.

Pharmacological treatment effects on eye movement control

The increasing use of eye movement paradigms to assess the functional integrity of brain systems involved in sensorimotor and cognitive processing in clinical disorders requires greater attention to effects of pharmacological treatments on these systems. This is needed to better differentiate disease and medication effects in clinical samples, to learn about neurochemical systems relevant for identified disturbances, and to facilitate identification of oculomotor biomarkers of pharmacological effects. In this review, studies of pharmacologic treatment effects on eye movements in healthy individuals are summarized and the sensitivity of eye movements to a variety of pharmacological manipulations is established. Primary findings from these studies of healthy individuals involving mainly acute effects indicate that: (i) the most consistent finding across several classes of drugs, including benzodiazepines, first- and second- generation antipsychotics, anticholinergic agents, and anticonvulsant/mood stabilizing medications is a decrease in saccade and smooth pursuit velocity (or increase in saccades during pursuit); (ii) these oculomotor effects largely reflect the general sedating effects of these medications on central nervous system functioning and are often dose-dependent; (iii) in many cases changes in oculomotor functioning are more sensitive indicators of pharmacological effects than other measures; and (iv) other agents, including the antidepressant class of serotonergic reuptake inhibitors, direct serotonergic agonists, and stimulants including amphetamine and nicotine, do not appear to adversely impact oculomotor functions in healthy individuals and may well enhance aspects of saccade and pursuit performance. Pharmacological treatment effects on eye movements across several clinical disorders including schizophrenia, affective disorders, attention deficit hyperactivity disorder, Parkinson's disease, and Huntington's disease are also reviewed. While greater recognition and investigation into pharmacological treatment effects in these disorders is needed, both beneficial and adverse drug effects are identified. This raises the important caveat for oculomotor studies of neuropsychiatric disorders that performance differences from healthy individuals cannot be attributed to illness effects alone. In final sections of this review, studies are presented that illustrate the utility of eye movements for use as potential biomarkers in pharmacodynamic and pharmacogenetic studies. While more systematic studies are needed, we conclude that eye movement measurements hold significant promise as tools to investigate treatment effects on cognitive and sensorimotor processes in clinical populations and that their use may be helpful in speeding the drug development pathway for drugs targeting specific neural systems and in individualizing pharmacological treatments.

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.

Psychomotor impairment and cognitive disturbances induced by neuroleptics

Reviews of the literature have failed to demonstrate any consistent effects of typical or atypical neuroleptics on psychomotor or cognitive function in schizophrenic patients. Better methods and study designs are required, and healthy volunteer studies are necessary to control for variables due to schizophrenic psychopathology. Eye movements are a sensitive, reliable and relatively pure measure of attention and arousal. Two volunteer studies of the effects of single doses of haloperidol (2,4 and 6 mg), chlorpromazine (50 mg) and remoxipride (100 and 150 mg) on saccadic and smooth pursuit eye movements are described. All drugs impaired both eye movement measures, but the doses used were not clinically equivalent. No available test is yet able to distinguish between benzodiazepines and neuroleptics.