- Most brain imaging studies of acute cannabis exposure have relied on positron emission tomography, which exposes subjects to radiation
- fNIRS may be a safer, viable option for such research
- After oral administration of THC, oxygenated hemoglobin concentration increased in several channels on the prefrontal cortex during working memory tasks
- Although their results are preliminary, future research may be able to make use of fNIRS to investigate the time-course of acute cannabis intoxication and recovery
Double-blind, placebo-controlled studies have established that oral administration of delta 9-tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis, acutely impairs performance on memory, attention, reaction time, visual tracking and motor function tasks. The prefrontal cortex is heavily involved in many of those tasks, so to understand how cannabis affects cognitive performance, scientists study THC’s impact on blood flow in that part of the brain.
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Most brain imaging studies of acute cannabis exposure have relied on positron emission tomography, which exposes subjects to radiation. In Frontiers in Human Neuroscience, researchers led by Jodi M. Gilman, PhD, director of neuroscience at the Center for Addiction Medicine at Massachusetts General Hospital, and Hasan O. Keles, PhD, report on their preliminary study that found functional near-infrared spectroscopy (fNIRS) was a feasible alternative.
The study followed 18 volunteers, ages 18 to 55, who reported using cannabis at least weekly. The participants underwent two sessions of fNIRS while they completed tests of working memory. The first imaging was conducted before the participants received a single dose of dronabinol (an FDA-approved synthetic THC) and the other about two hours later at the time of peak pharmacokinetic effects of dronabinol.
Five participants had to be excluded from the final analysis. Three of them could receive only a very low dose of dronabinol because their baseline blood pressure was >140/90. For the other two, there were heavy motion artifacts in the fNIRS signal.
Data on the remaining 13 participants showed a significant increase in the oxygenated hemoglobin concentration after THC administration in several channels on the prefrontal cortex. This finding is consistent with most brain imaging studies of smoked or orally administered cannabis.
Participants did not demonstrate significantly impaired performance on the working memory tests, which the researchers attribute to the small sample size.
The researchers comment that, in addition to not exposing people to radiation, fNIRS is portable, noninvasive, economical and can be used repeatedly throughout the day on a single participant. The researchers suggest that although caution is needed in interpreting their preliminary findings, future research may be able to make use of fNIRS to investigate the time-course of acute cannabis intoxication and recovery.
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