Title:Brain Imaging Studies on the Cognitive, Pharmacological and Neurobiological Effects of Cannabis in Humans: Evidence from Studies of Adult Users
Volume: 22
Issue: 42
Author(s): Aviv Weinstein, Abigail Livny and Abraham Weizman
Affiliation:
Keywords:
Cannabis, marijuana, THC, cannabidiol, brain imaging, fMRI, dopamine.
Abstract: Cannabis is the most widely used illicit drug worldwide. Regular cannabis use has
been associated with a range of acute and chronic mental health problems, such as anxiety,
depression, psychotic symptoms and neurocognitive impairments and their neural mechanisms
need to be examined. This review summarizes and critically evaluates brain-imaging
studies of cannabis in recreational and regular cannabis users between January 2000 and
January 2016. The search has yielded eligible 103 structural and functional studies. Regular
use of cannabis results in volumetric, gray matter and white matter structural changes in the
brain, in particular in the hippocampus and the amygdala. Regular use of cannabis affects
cognitive processes such as attention, memory, inhibitory control, decision-making, emotional
processing, social cognition and their associated brain areas. There is evidence that
regular cannabis use leads to altered neural function during attention and working memory
and that recruitment of activity in additional brain regions can compensate for it. Similar to
other drugs of abuse, cannabis cues activated areas in the reward pathway. Pharmacological studies showed a
modest increase in human striatal dopamine transmission after administration of THC in healthy volunteers.
Regular cannabis use resulted in reduced dopamine transporter occupancy and reduced dopamine synthesis but
not in reduced striatal D2/D3 receptor occupancy compared with healthy control participants. Studies also showed
different effects of Δ-9 tetrahydrocannabinol (THC) and cannabidiol (CBD) on emotion, cognition and associated
brain regions in healthy volunteers, whereby CBD protects against the psychoactive effects of THC. Brain imaging
studies using selective high-affinity radioligands for the imaging of cannabinoid CB1 receptor availability in
Positron Emission Tomography (PET) showed downregulation of CB1 in regular users of cannabis. In conclusion,
regular use of the cannabinoids exerts structural and functional changes in the human brain. These changes have
profound implications for our understanding of the neuropharmacology of cannabis and its effects on cognition,
mental health and the brain.
