Background: The aim of this study was to identify the neural correlates of each component of the clock drawing test (CDT) in drug-naïve patients with Alzheimer's disease (AD) using single photon emission computed tomography.

Methods: The participants were 95 drug-naïve patients with AD. The Rouleau CDT was used to score the clock drawings. The score for the Rouleau CDT (R total) is separated into three components: the scores for the clock face (R1), the numbers (R2), and the hands (R3). A multiple regression analysis was performed to examine the relationship of each score (i.e. R total, R1, R2, and R3) with regional cerebral blood flow (rCBF). Age, gender, and education were included as covariates. The statistical threshold was set to a family-wise error (FWE)-corrected p value of 0.05 at the voxel level.

Results: The R total score was positively correlated with rCBF in the bilateral parietal and posterior temporal lobes and the right middle frontal gyrus. R1 was not significantly positively correlated with rCBF, R2 was significantly positively correlated with rCBF in the right posterior temporal lobe and the left posterior middle temporal lobe, and R3 was significantly positively correlated with rCBF in the bilateral parietal lobes, the right posterior temporal lobe, the right middle frontal gyrus, and the right occipital lobe.

Conclusions: Various brain regions were associated with each component of the CDT. These results suggest that an assessment of these components is useful for the detection of localization of brain damage.