Earlier Cannabis Use Was Linked to Slower Reaction Times in Adulthood Through Brain Encoding Changes

Earlier cannabis age of onset was associated with longer reaction times and reduced posterior parietal cortex activation during encoding, which mediated the age-of-onset effect. However, age-of-onset associations did not differ between single-use and repeated-use groups. Greater total cannabis use was associated with increased DLPFC activation during maintenance. Surprisingly, cannabis users generally performed better than never-users.

75 adults with longitudinal cannabis use assessments and prenatal drug exposure data completed a spatial working memory task during fMRI at age 28. All passed same-day drug screens. Fast event-related design separated encoding, maintenance, and retrieval phases.

This study provides a nuanced picture: while earlier cannabis onset affects brain activation patterns during memory encoding, the finding that even single use showed the same pattern as repeated use suggests these differences may reflect pre-existing risk factors rather than cannabis-caused damage.

The finding that cannabis users performed better than never-users, and that single and repeated use showed the same age-of-onset patterns, challenges simple narratives about cannabis "damaging" the brain. The reality appears more complex, involving pre-existing differences in neurocognitive systems.

Small never-user group (n=15). Cannot fully separate cannabis effects from pre-existing risk factors. Prenatal drug exposure in many participants adds complexity. Cross-sectional brain imaging cannot establish causation.