Non-invasive brain imaging accurately identifies drivers under influence of THC

With the rapid rise in marijuana use, keeping roads safe from drivers who get behind the wheel while high has become of increasing concern. For years, there has been little that could be done to identify and enforce driving while impaired. But a recent study from researchers at Massachusetts General Hospital (MGH) has found that non-invasive brain imagining can accurately identify people with impaired performance due to THC, the psychoactive ingredient in cannabis that causes a “high.”

As more and more states legalize cannabis, the need for a portable, accurate brain imaging technique that identifies levels of THC impairment and intoxication has grown more pressing. This new technique measures brain activation patterns seen in people impaired by THC intoxication by utilizing a kind of imaging technology called functional near-infrared spectroscopy (fNIRS). Implementation of this method for identifying impairment could significantly benefit road and workplace safety. 

“Our research represents a novel direction for impairment testing in the field,” says lead author Jodi Gilman, an investigator with MGH’s Center for Addiction Medicine, in a statement. “Our goal was to determine if cannabis impairment could be detected from activity of the brain on an individual level. This is a critical issue because a ‘breathalyzer’ type of approach will not work for detecting cannabis impairment, which makes it very difficult to objectively assess impairment from THC during a traffic stop.”

Safe driving relies heavily on cognitive and psychomotor performance, which studies have shown are impaired while under the influence of THC. However, the body’s concentration of THC does not necessarily correlate with functional impairment. Regular users of cannabis may be able to function unimpaired, even with high levels of THC in the body. Metabolites of THC can be traced through the bloodstream even weeks after it is last used and its effects have faded. 

In the hopes of identifying a reliable method of determining THC impairment from intoxication, researchers at MGH had 169 cannabis users undergo fNIRS brain imaging prior to and after consuming oral THC or a placebo. Participants who received oral THC and experienced intoxication showed a marked increase in oxygenated hemoglobin concentration (HbO)—a signature of neural activity in the prefrontal cortex of the brain—compared to participants who experienced little to no symptoms of intoxication. 

“Identification of acute impairment from THC intoxication through portable brain imaging could be a vital tool in the hands of police officers in the field,” said senior author and principal investigator A. Eden Evins, MD, MPH, founding director of the Center for Addiction Medicine. “The accuracy of this method was confirmed by the fact that impairment determined by machine learning models using only information from fNIRS matched self-report and clinical assessment of impairment 76 percent of the time.”

MGH researchers did not test the usage of fNIRS in roadside impairment assessments, but they did state that developing a device using this technique would be highly advantageous. It is possible to create portable, battery-powered, and relatively inexpensive devices that employ fNIRS techniques and allow for storing or wireless transmission of data. It would also be possible to create a headband or cap with fNIRS technology for roadside use. 

“Companies are developing breathalyzer devices that only measure exposure to cannabis but not impairment from cannabis. We need a method that won’t penalize medical marijuana users or others with insufficient amounts of cannabis in their system to impair their performance,” Gilman said. “While it requires further study, we believe brain-based testing could provide an objective, practical and much needed solution.”

This study was published in the journal Neuropsychopharmacology.

Article written by Anna Landry

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