Associations between regular cannabis use and brain resting-state functional connectivity in adolescents and adults.

Background/aim: Cannabis use is highly prevalent in adolescents; however, little is known about its effects on adolescent brain function.

Method: Resting-state functional magnetic resonance imaging was used in matched groups of regular cannabis users ( = 70, 35 adolescents: 16-17 years old, 35 adults: 26-29 years old) and non-regular-using controls ( = 70, 35 adolescents/35 adults). Pre-registered analyses examined the connectivity of seven major cortical and sub-cortical brain networks (default mode network, executive control network (ECN), salience network, hippocampal network and three striatal networks) using seed-based analysis methods with cross-sectional comparisons between user groups and age groups.

Results: The regular cannabis use group (across both age groups), relative to controls, showed localised increases in connectivity only in the ECN analysis. All networks showed localised connectivity differences based on age group, with the adolescents generally showing weaker connectivity than adults, consistent with the developmental effects. Mean connectivity across entire network regions of interest (ROIs) was also significantly decreased in the ECN in adolescents. However, there were no significant interactions found between age group and user group in any of the seed-based or ROI analyses. There were also no associations found between cannabis use frequency and any of the derived connectivity measures.

Conclusion: Regular cannabis use is associated with changes in connectivity of the ECN, which may reflect allostatic or compensatory changes in response to regular cannabis intoxication. However, these associations were not significantly different in adolescents compared to adults.