Interestingly, during the viewing of masked happy faces, a similar pattern of activation as to that demonstrated for masked angry faces was detected for both subject groups (see Table 4). Non-marijuana smoking control subjects demonstrated a small focal area of increased activity within the cingulate gyrus relative to the chronic, heavy marijuana smokers (peak x, y, z = 4, 26, 36; t = 2.12, p< 0.05; k = 30; see Figure 3a), while marijuana smokers showed greater activation within mid (x, y, z = 20, −10, 42; t = 3.62, p< 0.05; k =43) and posterior cingulate (x, y, z, = 20,−40, 30; t = 3.46, p< 0.05; k = 44) regions relative to the control subjects (see Figure 3b). Within the amygdala, non-marijuana smoking control subjects demonstrated small areas of increased activity bilaterally relative to the chronic, heavy marijuana smokers (x, y, z = 26, 2, −20; t = 2.64, p< 0.05; k =24; see Figure 4a), while marijuana smokers again showed no increased activity relative to the control subjects in this region (see Figure 4b).
