A deficit profile of executive, memory, and motor functions in schizophrenia

This study examined the neuropsychological deficits associated with schizophrenia and the interrelationships among multiple dissociable cognitive and motor functions. The tests were selected for their previously demonstrated sensitivity to circumscribed brain pathology and included four functional domains: executive functions, short-term memory and production, motor ability, and declarative memory. Each test composite was divided according to verbal versus nonverbal material or left- versus right-hand performance; this distinction permitted functions principally subserved by the left or right cerebral hemispheres to be tested separately. Data reduction was theoretically driven by the test selection and was achieved first by standardizing the scores of each test for age-related differences observed in the normal control group, and then by calculating test composite scores as an average of the age-corrected Z-scores of the tests comprising a functional composite. The schizophrenic group was impaired equivalently on all composites for both cerebral hemispheres; on average, the Z-scores of the patients were 1 standard deviation below those of the control group. The cognitive test composite scores were highly intercorrelated but showed only weak associations with motor ability. Multiple regression analyses suggested that symptom severity was a significant predictor of the Declarative Memory and Short-Term Memory/Production composite scores after accounting for disease duration, whereas disease duration uniquely contributed to the Executive Functions composite scores after controlling for symptom severity. Even though the schizophrenics as a group showed an equivalent level of deficit across all test composites, 1) the deficits were associated with different aspects of psychiatric symptomatology, 2) the motor deficit was independent of the cognitive deficits, and 3) each neuropsychological domain contributed independently to the deficit pattern. Thus, what appears to be a generalized functional deficit in schizophrenia may actually be, at least in part, combinations of multiple specific deficits.