Eye-tracking performance and adaptive functioning over the short-term course of first-episode psychosis

Towards Clinically Relevant Oculomotor Biomarkers in Early Schizophrenia

In recent years, psychiatric research has focused on the evaluation and implementation of biomarkers in the clinical praxis. Oculomotor function deviances are among the most consistent and replicable cognitive deficits in schizophrenia and have been suggested as viable candidates for biomarkers. In this narrative review, we focus on oculomotor function in first-episode psychosis, recent onset schizophrenia as well as individuals at high risk for developing psychosis. We critically discuss the evidence for the possible utilization of oculomotor function measures as diagnostic, susceptibility, predictive, monitoring, and prognostic biomarkers for these conditions. Based on the current state of research we conclude that there are not sufficient data to unequivocally support the use of oculomotor function measures as biomarkers in schizophrenia.

Sinusoidal smooth pursuit eye tracking at different stimulus frequencies: position error and velocity error before catch-up saccades in schizophrenia and in major depressive disorder

OBJECTIVE

The aim of the present study was to ascertain the extent of impairment of position error and velocity error processing in eye tracking dysfunction in schizophrenic and depressive patients.

METHOD

A total of 21 schizophrenic and 19 unipolar depressive patients and 21 healthy controls were subjected to an eye tracking test with electro-oculography using horizontal sinusoidal stimuli with frequencies of 0.2-0.7 Hz. Position error and velocity error were measured over a saccade-free range of 200 ms before catch-up saccades at 50 ms intervals.

RESULTS

For position error, the schizophrenia patients displayed increased values particularly compared to controls, more rarely compared to depressive patients, depending on the stimulus frequency used. The increase in stimulus frequency did not lead to an increase in position error in any group of subjects over a prolonged period. For velocity error, in contrast, the study groups differed only in a few, isolated pre-saccadic intervals. The increase in stimulus frequency, however, led to an increase in velocity error in the schizophrenia patients over the entire 200 ms interval. The depressive patients did not differ notably from the controls, neither in terms of position error nor velocity error.

CONCLUSIONS

Eye tracking dysfunction in schizophrenia can be described as follows with regard to position error and velocity error: On the one hand, there is an increased position error tolerance largely independent of stimulus frequency, possibly due to an impairment of processing localization information. On the other hand, velocity processing is more severely impaired by an increase in stimulus frequency.

Effects of procyclidine on eye movements in schizophrenia

Smooth pursuit eye movement (SPEM) and antisaccade deficits are observed in the schizophrenia spectrum and have been used to study the pathophysiology as well as the genetic basis of this condition. The neurotransmitter acetylcholine has been implicated in a number of cognitive processes thought to underlie SPEM and antisaccade performance. This study investigates effects on eye movements of procyclidine, an anticholinergic drug often administered to schizophrenic patients. A total of 13 patients completed a double-blind placebo-controlled crossover design, receiving 15 mg procyclidine and placebo. Seven participants received procyclidine first and placebo second, six participants were tested in the reverse order. SPEM and antisaccade (as well as fixation and prosaccade) eye movements were recorded using infrared oculography. Results showed that procyclidine overall, relative to placebo, mildly worsened SPEM performance, as indicated by nonsignificantly reduced gain (p=0.08) and increased frequency of intrusive anticipatory saccades during pursuit (p=0.06). A significant interaction of group and order of administration indicated that procyclidine increased the rate of antisaccade reflexive errors only when administered first; the opposite pattern was observed when placebo was administered first, likely due to the operation of practice effects at second assessment. These findings indicate that acute administration of a clinically relevant dose of procyclidine leads to mild impairments in eye movement performance in schizophrenic patients, suggesting the need to consider this compound in oculomotor studies in schizophrenia. The action of this anticholinergic drug on oculomotor performance is consistent with the hypothesized role of the cholinergic system in the cognitive mechanisms of attention and working memory, processes thought to underlie SPEM and antisaccade performance. Effects of order of administration and practice on the antisaccade task suggest that these factors need to be taken into consideration in future pharmacological studies.

Psychopathology and the binding problem

Normal cerebral activity is based on the rapid and flexible alternation of an enormous quantity of spatial-temporal patterns of neuronal firing. There is still much to learn about the mechanism that keeps neurons on functionally closed assemblies firing in synchronization. The explanation of this mechanism is the so called 'binding problem', one of the cornerstones of the generation of perceptions, cognitions, emotions and behaviours by the brain, and therefore of great interest to psychiatry. We explore the possibility that a 'binding dysfunction' could be a relevant aspect of the pathophysiology of mental disorders, and apply it to schizophrenia, in an attempt to integrate some neurobiological findings in this disorder, including a few preliminary data obtained with transcranial magnetic stimulation (TMS).