Objective: Both neuropsychological impairment and neurological soft signs have been documented in at least a subset of patients with schizophrenia. The purpose of the present study was to examine the relationship between soft signs and neuropsychological performance in patients with schizophrenia in order to address the issue of whether soft signs are related to global or more selective cognitive impairment.
Method: Patients with a DSM-III-R diagnosis of schizophrenia (N=176) were given a standardized neuropsychological battery and underwent a neurological examination. The study group was dichotomized on the basis of presence or absence of neurological soft signs.
Results: Patients with neurological soft signs (N=68) demonstrated significantly poorer performance on neuropsychological tasks that assessed timed motor speed and motor coordination (e.g., finger tapping, the Purdue Pegboard task, and part B of the Trail Making Test). These findings continued to be significant even after lifetime medication exposure, extrapyramidal symptoms, and abnormal involuntary movements were used as covariates.
Conclusions: These findings support the notion that soft signs are a manifestation of a localizable behavioral deficit of the systems that are involved in motor speed, coordination, and sequencing and are not indicative of global cognitive impairment. The specific deficit in motor abilities is consistent with the types of neurological soft signs that are most frequently reported and suggests involvement of frontal/subcortical circuitry in schizophrenia.