Brain imaging study shows how THC in cannabis disrupts brain activity and may cause cognitive impairment

A new study led by investigators from Massachusetts General Hospital reveals that the main psychoactive component in cannabis or marijuana disrupts the normal connections and activity of the brain’s prefrontal cortex, a region that is crucial for decision-making and self-control.

The findings are published in the Neuropsychopharmacology.

“We know that Δ9-tetrahydrocannabinol, or THC, in cannabis can affect thinking and behavior and potentially lead to cognitive impairment,” said senior author Jodi M. Gilman, Ph.D., director of Neuroscience at the Massachusetts General Hospital Center for Addiction Medicine and an associate professor in Psychiatry at Harvard Medical School. “This disruption of the prefrontal cortex may underlie cognitive impairment.”

Gilman and her colleagues conducted a double-blind, randomized, cross-over study in adults, aged 18–55 years, who used cannabis regularly. Using portable brain scanning technology, the researchers compared 128 participants’ brain activity under the influence of THC versus placebo.

THC was associated with decreased functional connectivity within the prefrontal cortex relative to placebo, with the weakest connections among those who reported greater severity of intoxication.

Also, THC was associated with increased variability (or reduced stability) of functional connectivity of the prefrontal cortex, which could indicate a reduced ability of the brain to efficiently adapt or reconfigure to changing stimuli. Finally, THC was associated with lower overall activity within the prefrontal cortex.

“We were able to measure these effects of THC intoxication using portable imaging, which could potentially be incorporated in impairment testing scenarios, for example at the roadside,” said Gilman.

“We need more studies to understand how brain effects of acute THC intoxication relate to cognitive performance and operational impairment.”