Brain activation to negative stimuli mediates a relationship between adolescent marijuana use and later emotional functioning

• Adolescent marijuana use and emotional functioning across time points were examined.
• Resiliency increased in controls but not heavy marijuana users across time points.
• Negative emotionality decreased in controls but not heavy marijuana users across time points.
• Heavy marijuana users had blunted brain activity to negative words relative to controls.
• Brain activity mediated the effect of marijuana use on later emotional functioning.

This work investigated the impact of heavy marijuana use during adolescence on emotional functioning, as well as the brain functional mediators of this effect. Participants (n = 40) were recruited from the Michigan Longitudinal Study (MLS). Data on marijuana use were collected prospectively beginning in childhood as part of the MLS. Participants were classified as heavy marijuana users (n = 20) or controls with minimal marijuana use. Two facets of emotional functioning—negative emotionality and resiliency (a self-regulatory mechanism)—were assessed as part of the MLS at three time points: mean age 13.4, mean age 19.6, and mean age 23.1. Functional neuroimaging data during an emotion-arousal word task were collected at mean age 20.2. Negative emotionality decreased and resiliency increased across the three time points in controls but not heavy marijuana users. Compared with controls, heavy marijuana users had less activation to negative words in temporal, prefrontal, and occipital cortices, insula, and amygdala. Activation of dorsolateral prefrontal cortex to negative words mediated an association between marijuana group and later negative emotionality. Activation of the cuneus/lingual gyrus mediated an association between marijuana group and later resiliency. Results support growing evidence that heavy marijuana use during adolescence affects later emotional outcomes.