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A brain-based approach for determining cannabis intoxication impairment


A recent research suggests that using functional near-infrared spectroscopy to image brain activity might provide a more accurate and consistent technique to identify impairment from cannabis intoxication.

A noninvasive brain imaging approach developed by researchers at Massachusetts General Hospital (MGH) has been demonstrated to be an objective and reliable way to identify those whose performance has been harmed by THC, the psychoactive element in cannabis. The method employs functional near-infrared spectroscopy (fNIRS), an imaging tool that measures brain activity patterns that are linked to impairment from THC intoxication. According to a study published in the journal Neuropsychopharmacology, the treatment might improve highway and workplace safety.

Because of the rising use of cannabis as a result of its legalization, there is an urgent need for a portable brain imaging technology that can discriminate between impairment and moderate THC intoxication. Jodi Gilman, PhD, investigator at the MGH Center for Addiction Medicine, adds, “Our study provides a unique avenue for impairment testing in the field.” “Our objective was to see whether cannabis impairment might be diagnosed on an individual basis via brain activity. This is a key problem since a ‘breathalyzer’ technique will not identify cannabis impairment, making objectively assessing THC impairment during a traffic stop very challenging.”

THC has been found in previous research to impair cognitive and psychomotor performance, all of which are required for safe driving, a factor that is considered to at least double the risk of fatal car accidents. The problem for scientists, however, is that THC levels in the body do not always equate to functional impairment. One explanation for this is that persons who use cannabis often might have high THC levels in their bodies without being affected. Another is that THC metabolites may stay in the system for weeks after the last cannabis usage, much longer than the intoxication time. As a result, a new approach for determining impairment from cannabis intoxication is required.

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169 cannabis users participated in the MGH trial, which included fNIRS brain imaging before and after taking either oral THC or a placebo. In comparison to individuals who reported mild or no intoxication after being administered oral THC, those who reported intoxication had a higher oxygenated hemoglobin content (HbO), which is a form of neural activity signature from the prefrontal cortex area of the brain.

“Identifying acute impairment from THC intoxication using portable brain imaging might be a key tool in the hands of police officers in the field,” says A. Eden Evins, MD, MPH, founding director of the Center for Addiction Medicine, senior author and lead investigator. “The accuracy of this technique was proven by the fact that machine learning models 76 percent of the time detected impairment using just information from fNIRS matched self-report and clinical evaluation of impairment.”

While the research did not directly evaluate fNIRS in roadside evaluations of impaired driving, it did point to a number of benefits for such a use. These include the viability of low-cost, battery-powered fNIRS systems that enable data to be saved on worn recording units or wirelessly sent to a laptop. Furthermore, fNIRS technology might be built onto a headband or hat, requiring very little setup time.

“Companies are creating breathalyzer devices that simply assess cannabis exposure, not cannabis impairment,” Gilman adds. “We need an approach that doesn’t punish medicinal marijuana users or those who don’t have enough THC in their system to impede their performance. While we feel that further research is required, we believe that brain-based testing might give an objective, practical, and much-needed answer.”

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Gilman is a psychiatry associate professor at Harvard Medical School. At Harvard Medical School, Evins is the Cox Family Professor of Psychiatry.

The National Institute on Drug Abuse financed the research.

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