Abnormal medial prefrontal cortex activity in heavy cannabis users during conscious emotional evaluation.

Long-term heavy cannabis users who are not acutely intoxicated show diminished brain responses in the medial prefrontal cortex (mPFC) when consciously evaluating emotional images, compared to non-users. Both groups judged the same stimuli as emotional and had similar activations in visual, midbrain, and middle cingulate cortices. However, controls showed additional amygdalar and inferior frontal gyrus activations, while cannabis users showed mPFC deactivations during emotional evaluation. Between-group comparisons found mPFC activity during positive and negative evaluation was significantly hypoactive in cannabis users. This abnormal neural processing of affective content extends to conscious evaluation and resembles attenuated mPFC responses found during increased non-affective cognitive load.

Study at a glance

Abstract

Long-term heavy cannabis users (cannabis users) who are not acutely intoxicated have diminished subconscious neural responsiveness to affective stimuli. This study sought to determine if abnormal processing extends to the conscious evaluation of emotional stimuli. Functional magnetic resonance imaging (fMRI) was used to examine brain activity as cannabis users (N = 16) and non-cannabis-using controls (N = 17) evaluated and categorized standardized International Affective Picture System (IAPS) stimuli. Individual judgments were used to isolate activity during the evaluation of emotional (i.e., emotional evaluation) or neutral (i.e., neutral evaluation) stimuli. Within- and between-group analyses were performed. Both groups judged the same stimuli as emotional and had activations in visual, midbrain, and middle cingulate cortices during emotional evaluation, relative to neutral. Within-group analyses also revealed amygdalar and inferior frontal gyrus activations in controls, but not cannabis users, and medial prefrontal cortex (mPFC) deactivations in cannabis users, but not controls, during emotional evaluation, relative to neutral. Between-group comparisons found that mPFC activity during positive and negative evaluation was significantly hypoactive in cannabis users, relative to controls. Abnormal neural processing of affective content extends to the level of consciousness in cannabis users. The hypoactive mPFC responses observed resembles the attenuated mPFC responses found during increased non-affective cognitive load in prior research. These findings suggest that abnormal mPFC singling in cannabis users during emotional evaluation might be associated with increased non-affective cognitive load.