regions in the chronic, heavy marijuana smokers relative to the non-smoking control subjects may suggest a disruption early in the network responsible for detection and early processing of stimuli, which is then further reflected in the altered cingulate response to the masked faces. The positive association noted between number of smokes per week and amygdalar activity during the viewing of masked happy stimuli despite the relative lack of activity noted in the region when compared to non-smoking healthy controls suggests that the use of marijuana may lead to a system-wide alteration in inhibitory/excitatory circuitry which engages both cingulate and amygdalar regions. It is also possible that increased marijuana use may result in reduced inhibitory function for positive stimuli and increased inhibitory function for negative stimuli therefore modulating response within fronto-limbic regions. This may help to explain why marijuana smokers often report increased feelings of relaxation and affiliatory behavior after smoking (Green et al., 2003).
