Motor abnormalities occur in schizophrenia (SZ) and may arise from striatal
dysfunction. This study examined whether the pattern of performance on sim
ple and complex motor abilities. in SZ was similar to that of patients with
Parkinson's disease (PD). Quantitative tests of speeded movement and motor
and cognitive sequencing were used to assess 25 SZ, 16 PD, and 84 normal c
ontrols (NCs). Sequencing performance was also examined with motor rigidity
taken into account. Compared with the NC group, the SZ and PD groups were
impaired on measures of motor rigidity and motor sequencing. With rigidity
accounted for, the SZ group was significantly more impaired than the PD gro
up on motor sequencing; cognitive and motor processes contributed to the mo
tor deficit. Cognitive sequencing performance predicted motor sequencing pe
rformance in PD but not SZ. Although both SZ and PD resulted in significant
motor and cognitive sequencing deficits, the pattern and correlates of the
se deficits differ, suggesting that the affected neural systems underlying
motor deficits in SZ are different from those involved in PD.