Fig. 2. Relative regional cerebral blood flow (rCBF) increases (A ) and decreases (B ) comparing low and moderate conditions. (Top ) The relative rCBF increases (A ) to the left and decreases (B ) to the right displayed on a magnetic resonance image surface rendering. (Bottom ) The design matrices of the general linear model used to partition the data (seven blocks corresponding to seven subjects, and seven blocks consisting of nine effects with global activity as covariate of no interest). Threshold was set at P = 0.0006 for peak z  values and a minimum of 25 voxels in extension. Color code identifies rCBF increases (from minimum to maximum scores) or decreases (from minimum to maximum scores) during the low dose in comparison to control (values in table 3).