Smooth pursuit eye movement (SPEM) abnormalities in schizophrenia, although well described, are poorly understood. SPEMs are initiated by motion of an object image on the retina. During initiation, the eyes accelerate until they approximate target velocity and a state of minimal retinal motion is achieved. Pursuit is maintained through predictive eye movements based on extraretinal signals and corrections based on deviations from the fovea. Here, initiation and predictive pursuit responses were used to estimate the contributions of retinal and extraretinal signals to pursuit maintenance in schizophrenia patients' relatives. Relatives exhibited normal initiation, but had lower predictive pursuit gain compared with controls. Relatives had normal gain during pursuit maintenance, presumably by greater reliance on retinal error. This was confirmed by group differences in regression coefficients for retinal and extraretinal measures, and suggests that schizophrenia SPEM deficits involve reduced ability to maintain or integrate extraretinal signals, and that retinal error may be used to compensate.
DescriptorsSmooth pursuit eye movements; Schizophrenia; Predictive pursuit; Extra-retinal processing; Smooth pursuit initiation A wealth of evidence, including a recent preliminary report citing linkage of pursuit abnormality to chromosome 6p21 in relatives of schizophrenic patients, suggests that the smooth pursuit deficit marks the genetic liability to schizophrenia (Arolt et al., 1996;Clementz & Sweeney, 1990;Levy, Holzman, Matthysse, & Mendell, 1994). Although many aspects of the smooth pursuit deficit associated with the schizophrenia phenotype(s) have been well described, only recently have investigators focused on understanding the underlying neuronal mechanisms of these eye movement abnormalities (Clementz & McDowell, 1994;Ross et al., 1995;Sweeney et al., 1998). The smooth pursuit function is a highly developed and complex system served by a widely distributed neuronal network (Leigh & Zee, 1991). In recent years, many of the normal functions of the component processes of the smooth pursuit system in humans, and the underlying neurophysiological substrates in monkeys, have become known (Assad & Maunsell, 1995;Barnes, Barnes, & Chakraborti, 2000;Barton et al., 1996;Komatsu & Wurtz, 1989;Krauzlis, 2001; MacAvoy, Gottlib, & Bruce, 1991; Newsome, Wurtz, Dersteler, & Mikami, 1985;Newsome, Wurtz, & Komatsu, 1988;Schmid, Rees, Frith, & Barnes, 2001;Suh, Leung, & Kettner, 2000). Examination of smooth pursuit in schizophrenia within a neurophysiology-based framework has an advantage over traditional methods, in that it is likely to identify specific brain regions that are associated with observed deficits. In addition, the identification of a functionally specific deficit is likely to be more sensitive and specific in identifying the phenotype compared with traditional global measures.Normally, the pursuit system needs motion information to generate smooth pursuit eye movements. During initiation of smooth pursuit, ...