SMOOTH-PURSUIT EYE-MOVEMENTS TO EXTRARETINAL MOTION SIGNALS - DEFICITS IN RELATIVES OF PATIENTS WITH SCHIZOPHRENIA

Background: Although mounting evidence supports the idea that smooth p ursuit abnormality marks the genetic liability to schizophrenia, the p recise ocular motor mechanism underlying the abnormality remains unkno wn. Based on recent findings in schizophrenia, we hypothesize that sub tle deficits in the ability to hold online and/or use extraretinal mot ion information underlie the pursuit abnormality in vulnerable individ uals. Methods: The hypothesis was tested in 69 first-degree, biologica l relatives of probands with schizophrenia; 26 relatives had schizophr enia spectrum personalities (SSP). Subjects recruited from the communi ty (n=71; 29 with SSP), without a known family history of psychosis, c onstituted the comparison groups. The traditional smooth pursuit gain measure, which is a ratio of smooth pursuit eye velocity in response t o both retinal and extraretinal motion signals and the target velocity , was obtained. In addition, newly developed measures of predictive sm ooth pursuit (ie, in the presence of only extraretinal motion signals) were obtained. The latter measures were evaluated after the current r etinal motion signals were made unavailable by briefly making the targ et invisible. Results: Relatives, particularly those with SSP, showed significantly poorer predictive pursuit response to extraretinal motio n signals (F-2,F-13o=6.51, P<.005), com pared with the community subje cts. However, the traditional smooth pursuit gain in response to both retinal and extraretinal motion signals was not different between grou ps. Conclusions: These results suggest that relatives of patients with schizophrenia, particularly those with SSP, have specific deficits in predictive pursuit based on only extraretinal motion signals, Normal smooth pursuit gain in response to both retinal and extraretinal motio n signals is likely due to compensation based on retinal motion inform ation. The latter suggests normal retinal motion processing and smooth pursuit motor output.