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Two studies on schizophrenia and motion perception
  
By
Edward R. Winstead


 

Schizophrenia is often accompanied by subtle changes in the perception of motion. The changes—such as an impaired ability to track moving objects—occur in many individuals with the disease and some of their relatives. They are apparent during visual testing but do not affect real-world activities like driving or hitting a baseball. Two new studies suggest that eye-movement disturbances run in families and may be useful markers in genetic studies of schizophrenia.

The first study confirms previous reports that performance on visual tests can be a reliable marker of schizophrenia. Researchers at the Nihon University School of Medicine in Tokyo evaluated visual acuity and responsiveness in patients with schizophrenia, depression, and healthy controls. Patients with schizophrenia could reliably be distinguished from depressed patients and controls based on the test results.

The testing strategy "detected schizophrenia irrespective of culture, race and various other subject variables," the researchers write in Schizophrenia Research. "Furthermore, it is indicative of the stable, significant difference that exists between subjects with and without schizophrenia."

In the second study, researchers at the University of Medical Sciences in Poznan, Poland, found an association between certain forms of the dopamine D3 receptor gene, or DRD3, and performance on visual exams. The vast majority of schizophrenic patients had some degree of eye-movement disturbances, as did one-quarter of the unrelated control subjects. Those with two copies of a version of DRD3 scored significantly worse on the exams than did others in the study.

"The findings of our study suggest a contribution of the DRD3 gene to the quality of eye tracking performance both in schizophrenic patients and healthy controls," the researchers write in Molecular Psychiatry. The study focused on the DRD3 gene because of published data suggesting a possible role for the gene in schizophrenia.

Some eye-tracking disturbances occur when 'smooth pursuit' eye movements—those used to track moving objects—are interrupted by rapid eye movements, which are normally used to read or look around. Why this happens is not known, but the trait clearly has a genetic component.

Keeping one's eye on a moving object is a complex neurological process that requires the integration of multiple brain regions, says Randy Ross, who studies the genetics of eye-movement disorders and schizophrenia at the University of Colorado Health Sciences Center in Denver. He points out that deficiencies in one region of the brain may be compensated for in another. "Thus, problems identified during a sophisticated test to measure a specific type of eye-movement performance may have no relation to real-world performance—because of other compensatory mechanisms," he says.

In the 1970s, Philip S. Holzman, now of Harvard University in Cambridge, Massachusetts, and others conducted the first studies to suggest that eye-tracking dysfunction can be inherited and is associated with schizophrenia.

See related GNN article
»A Theory of Schizophrenia, Viruses and Pregnancy

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Kojima, T. et al. Stability of exploratory eye movements as a marker of schizophrenia—a WHO multi-center study. Schizophr Res 52, 203-213 (December 1, 2001).
 
Rybakowski, J.K. et al. Dopamine D3 receptor (DRD3) gene polymorphism is associated with the intensity of eye movement disturbances in schizophrenic patients and healthy subjects. Mol Psychiatry 6, 718-724 (November 2001).
 

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