Neural Correlates of Impaired Performance on the Clock Drawing Test in Alzheimer’s Disease

Abstract

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.

Cerebral Substrates Related to Impaired Performance in the Clock-Drawing Test in Dementia with Lewy Bodies

“…To reveal neural substrates for CDT performance deficits in patients with DLB, we examined the relationship between CDT impairment and regional cerebral blood flow (CBF) measured by single photon emission computed tomography (SPECT). A previous SPECT study on AD showed that CDT performance has a close relationship with the left posterior temporal function, and that semantic memory deficit may contribute to impaired CDT performance in AD [7] . In contrast to AD, DLB is characterized by prominent deficits in attentional, executive and visual-perceptual function with lesser verbal memory/semantic knowledge impairments [2] .…”

“…Patients were divided into 2 groups based on their performance on the CDT: the impaired CDT group, which consisted of 30 patients who had a score of 0-3 on the CDT, and the normal CDT group, which consisted of 30 patients who had a normal CDT score (4 or 5) [7,10] . Severity of parkinsonism was assessed using the Hoehn and Yahr stages and a modified Unified Parkinson's Disease Rating Scale.…”

“…The CDT was administered and scored according to the modified Shulman method [7,10] . Briefly, patients were presented with a predrawn circle of 14-cm diameter on an A4 sheet of paper and a pencil, and the following instructions were given: 'This circle represents a clock face.…”

“…The MMSE score was included as a confounding covariate in the analysis. Age and education level were not considered as covariates because our previous study showed that neither age nor education level was correlated with CDT performance [7] . These analyses generated statistical parametric maps of the t statistic (SPM{t}), which were subsequently converted to unit normal distribution (SPM{Z}).…”

Clock Drawing in the Montreal Cognitive Assessment: Recommendations for Dementia Assessment

“…By contrast, individuals with less executive dysfunction relative to other domains of cognitive impairment (e.g. Alzheimer’s disease, AD) typically improve from command to copy [3,5,9,10,12,13]. Thus, when command and copy conditions are used together, clock drawing appears particularly helpful for differentiating dementia subtypes.…”