Neuropsychological similarities in lateralized parkinsonism.

Parkinson's disease (PD) patients who have left or right predominance of motor symptoms may exhibit cognitive differences. Previous research found greater neuropsychological impairment in patients with both right and left motor predominance, and some found no differences. Variability in overall severity of disease among the patients studied makes evaluation of these reports difficult. We examined the possibility that neuropsychological differences may occur in different stages of disease by comparing patients with mild unilateral disease (Exp. 1) and advanced disease (Exp. 2). Results indicated that while overall cognitive impairment increased with advancing disease, the pattern of neuropsychological impairments were not different with respect to laterality of motor symptoms in either experiment.