Neural correlates of impaired performance on the clock drawing test in Alzheimer's disease.

To identify the neural correlates for impaired performance on the clock drawing test (CDT) in patients with Alzheimer's disease (AD), we examined the relationship between the CDT performances and the regional cerebral blood flow (rCBF) in 100 AD patients. The patients were equally divided into a mildly impaired CDT group, a severely impaired CDT group, and two normal CDT groups, with age and dementia severity matched. Between-group comparisons revealed that rCBF reduction in the posterolateral region of the left temporal lobe was consistently associated with mild to severe impairment of the CDT in AD. Correlation analysis also showed that the rCBF in the left posterolateral temporal cortex was linearly correlated with CDT performance. The CDT scores in AD were significantly improved for the copy condition relative to the drawing-to-command condition. These findings suggest that CDT performance has a close relationship with the left posterior temporal function, and that semantic memory deficit may at least partly contribute to impaired CDT performance in AD.