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Although heritability estimates of schizophrenia are high, studies attempting to identify specific genes for schizophrenia have been only modestly successful. Strategies to improve the power of genetic studies include the creation of homogeneous subtypes of schizophrenia based on symptom presentation, and the identification of behavioural abnormalities that reflect the presence of genes for schizophrenia ("behavioural markers of risk") even in the absence of the full clinical disorder. Oculomotor abnormalities are one of the most well-documented markers of risk. It is not known whether abnormalities in motor control are specific to the oculomotor system or whether they are found as well in other domains such as skeletomotor control. It is also not known whether different types of schizophrenia-related symptoms, which presumably have distinct neural bases, are associated with different behavioural abnormalities. / This thesis investigates oculomotor and skeletomotor function in clinically unaffected individuals who are at elevated risk for schizophrenia based on their scores on either a positive-symptom schizotypy questionnaire (Perceptual Aberration Scale) (n = 21) or a negative-symptom schizotypy questionnaire (Physical Anhedonia) (n = 20), and in Controls (n = 29). / In Manuscript 1, we review the evidence suggesting that skeletomotor deficits are present in neuroleptic-naive schizophrenia patients and high-risk populations. The review supports the notion of skeletomotor dysfunction in these groups and underscores the lack of studies using instrumentation to characterize the deficits. In Manuscript 2, we compare the oculomotor performance of positive-symptom and negative-symptom schizotypes to that of controls. Results suggest that smooth pursuit deficits identify high-risk individuals with either positive or negative symptomatology, while antisaccade deficits identify primarily individuals with positive symptoms. In Manuscript 3, we use high-speed instrumentation and kinematic measures to evaluate skeletomotor function, and to assess the relationship between oculomotor and skeletomotor deficits in positive and negative-symptom schizotypes. This study revealed differential patterns of skeletomotor deficits in positive- and negative-symptom schizotypy, with both patterns suggestive of frontal-striatal dysfunction. In general, oculomotor and skeletomotor deficits were not associated. / Together these results support the notion of motor deficits across domains in risk for schizophrenia. In addition, they highlight the importance of distinguishing between positive and negative symptomatology when investigating the pathophysiology of risk for schizophrenia.

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Thesis (Ph.D.) - James Cook University, 2004. / Typescript (photocopy). Appendices: leaves 95-103. Bibliography: leaves 89-94.