(Regular cannabis use can shrink key brain regions) — A previous post of ours examined the correlation between cannabis use and intelligence; the study showed that cannabis use in adolescence had no impact on fluid intelligence. However, it was shown that cannabis use had a significant effect on crystallized intelligence. Today, we report on a new study that brings forth new evidence that cannabis use is actually associated with smaller volume in key brain areas.
The study looked at 111 participants who either had a long history (15.4 years) of cannabis use (twice a month with a minimal exposure to other illicit drugs) or were non-users.
The cannabis users included subgroups, determined by hair samples, that had been 1) using predominantly THC, 2) using THC in combination with CBD, and 3) taking a long period of abstinence (29 months) from both THC and CBD.
The researchers were interested in a particular region of the brain known as the hippocampus, with a purported involvement in a wide range of cognitive functioning. Most importantly, the hippocampus is known to be crucial for episodic memory(Tulving, 2002), spatial navigation(Maguire, 2000), and imagination(Mullally, 2013). As pictured below, the researchers were able to target this area in each participant and use a variety of scans to assess this region’s volume (i.e. how much space it takes up relative to the size of their brain), integrity (i.e. how well it’s organized on a neuronal level), and metabolic properties (i.e. cellular activity).
All participants underwent three types of MRI scans in order to make this possible A T1-weighted Structural scan (showing the white and grey matter throughout the brain), Diffusion Tensor imaging (DTI) scan (showing the preferred movement of water throughout the brain), and an N-acetylasparatate(NAA) Spectroscopic Imaging scan (showing key neurotransmitter concentrations). As an aside, DTI allows researchers to visualize the anatomical connectivity and integrity of both white and grey matter in the brain. It’s responsible for producing very sharp looking tractography images like in Muse’s album cover for The 2nd Law.
Essentially, this type of scan can show you how well certain areas of the brain are “wired up” and, thus, allow you to infer the structural efficacy of that region.
Thus, for each subject, the researchers had three neurological measures local to the hippocampal region. They wanted to see if these measured differed as a function of which group the subject was in: heavy cannabis use with THC, heavy cannabis use with THC and CBD, heavy cannabis users currently in a long-term abstinence, and non-cannabis users.
They found that current cannabis users, across the board, had smaller hippocampi and lower NAA concentrations—indicative of depreciated function. Thus, regular cannabis use can shrink key brain regions and render them less functional. The previous users who were in a long-term abstinence didn’t differ at all from the controls, though. This indicates that by refraining from smoking after heavy use, one can take advantage of the plastic nature of the brain and return to baseline. Additionally, the researchers found that for users that ingested a greater proportion of CBD had less drastic changes in both hippocampal shrinkage and NAA concentration decrease.
There was no effect found in DTI scans, insinuating that while volume and metabolic activity decreased, the infrastructure of the hippocampus remained in- tact.
In summary, using cannabis more than twice a month over a 15-month period does have significant effects on the structural and metabolic makeup of the hippocampus. However, since there was no root structural damage, as observed from the DTI findings, the damage may not be permanent. Specifically, a 29-month abstinence can negate these effects and consumption of CBD can help to prevent these negative side effects of cannabis. Thus, it would seem as though adding some Charlottes Web or ACDC, strains known for their high CBD to THC ratio – usually unpopular amongst recreational users due to their relative inability to produce a “head high”, could help to counteract the detrimental effects of heavy cannabis over prolonged periods of time.
Maguire, and Gadian (2000). Navigation-related structural change in the hippocampi of taxi drivers.
Mullally, S., and Maguire, E. (2013). Memory, Imagination, and Predicting the Future: A Common Brain Mechanism? The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry.
Tulving (2002). Episodic memory: from mind to brain.