Heavy cannabis users showed abnormally reduced medial prefrontal cortex activity when consciously evaluating both positive and negative emotional images, suggesting emotional processing is impaired even at the conscious level.
Read this if you use cannabis heavily and have noticed changes in emotional responsiveness or empathy.
mPFC activity during emotional evaluation was significantly hypoactive in heavy cannabis users for both positive and negative content.
What the researchers found
Researchers used fMRI to compare brain activity between 16 heavy cannabis users and 17 non-using controls as they evaluated emotional images from a standardized set (IAPS).
Both groups identified the same images as emotional and showed similar activation in visual, midbrain, and middle cingulate regions. But important differences emerged.
Control participants showed amygdala and inferior frontal gyrus activation during emotional evaluation. Cannabis users did not. Cannabis users showed medial prefrontal cortex (mPFC) deactivation during emotional processing. Controls did not.
Direct comparison confirmed that mPFC activity during both positive and negative emotional evaluation was significantly reduced in cannabis users. The researchers noted this pattern resembles what happens when people are under high cognitive load from non-emotional tasks, suggesting cannabis users may be expending more cognitive effort to process emotional information.
Why it matters
Previous research showed that cannabis users have diminished unconscious (subconscious) neural responses to emotional stimuli. This study extends the finding to conscious emotional evaluation, suggesting that the emotional processing deficit is pervasive rather than limited to automatic processing. This could affect relationships, empathy, and social functioning.
The numbers in context
16 heavy cannabis users vs 17 controls. Both groups agreed on which stimuli were emotional. Controls showed amygdala and IFG activation; users did not. Users showed mPFC deactivation; controls did not. Between-group: significant mPFC hypoactivation in users for both positive and negative evaluation.
How the study worked
Cross-sectional fMRI study. 16 heavy cannabis users and 17 non-using controls evaluated and categorized International Affective Picture System (IAPS) stimuli. Individual judgments were used to isolate brain activity during emotional versus neutral evaluation. Within-group and between-group analyses were performed.
What this study cannot tell us
Small sample size (16 and 17). Cross-sectional design cannot determine whether cannabis caused the changes or whether pre-existing differences led to cannabis use. Users were not acutely intoxicated, but chronic residual effects cannot be separated from withdrawal. The study does not report the duration or amount of cannabis use in detail.
How to read the evidence
Moderate evidence from a controlled neuroimaging study with appropriate comparison group and validated emotional stimuli.
When this study was published
Published in 2016. The emotional neuroscience of cannabis use continues to be investigated.
The bigger picture
The medial prefrontal cortex is crucial for emotional self-awareness, empathy, and social cognition. Its hypoactivation during emotional evaluation in cannabis users may contribute to the social and emotional difficulties sometimes reported by heavy users, even when they are not acutely intoxicated.
Questions still open
- Does the mPFC hypoactivation reverse with sustained abstinence? Does the amount or duration of cannabis use predict the degree of emotional processing deficit? Would this emotional blunting contribute to the "amotivation" sometimes attributed to cannabis use?
Common questions
Does cannabis affect emotional processing?
Does this mean cannabis makes you less emotional?
Read the original research
Abnormal medial prefrontal cortex activity in heavy cannabis users during conscious emotional evaluation.
Psychopharmacology, 233(6), 1035-44
Citation
Wesley, Michael J; Lile, Joshua A; Hanlon, Colleen A; Porrino, Linda J. (2016). Abnormal medial prefrontal cortex activity in heavy cannabis users during conscious emotional evaluation.. Psychopharmacology, 233(6), 1035-44. https://doi.org/10.1007/s00213-015-4180-y
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