“For so long, our model has been alcohol, so there’s been a lot of focus on breath and blood levels,” Dr.
Unlike the massive, electricity-hungry MRI scanning machines employed by hospitals, fNIRS is relatively portable; it measures the photon reflections from low-power LED bulbs mounted on a skullcap and shined into the skull.
“Essentially, the brain becomes more active but less efficient at processing, so the body gives it priority and sends more oxygen,” said Dr.
Next, the scientists trained a computer algorithm to spot the differences in oxygenated hemoglobin between those who were deemed high and those who were not.
Crucially, the system rarely indicated impairment in test subjects who consumed the THC-infused edibles yet were not deemed functionally impaired.
The scan results lend further credence to a wave of recent studies indicating that there is little if any connection between a given dose of THC, the level of marijuana metabolites in blood or saliva at a given time after use, and a particular level or even likelihood of impairment.
Taken together, those confounding factors mean traditional blood and saliva tests are barely more accurate than a coin toss at detecting impairment, according to Dr.
The researchers had initially planned to compare their experimental results to verdicts rendered by DREs, which proponents hail as the gold standard for assessing drug impairment.
Critics have warned the proposed law, under which drivers who refuse a blood test for cannabis metabolites would lose their licenses, is subjective, prone to officer bias, and would result in the arrests of innocent marijuana consumers.
One critical next step will be testing the system on a larger group of volunteers, in part to ensure that other drugs or health conditions don’t produce scan results that mimic those of stoned people.
“Officers need a better tool,” Evins said.
Dr.