Individuals who use cannabis before driving show impaired driving abilities and memory encoding, University of Iowa researchers found.

UI scientists used driving simulations and EEG tests to analyze markers of impaired driving ability in marijuana users using medical cannabis, which is legal in Iowa.

The National Institutes of Health, the UI, and Advanced Brain Monitoring’s researchers used cognitive tasks and a simulated driving test on their subjects to find brain signatures that correlate to impaired driving ability.

Timothy Brown, director of drugged driving research at the National Advanced Driving Simulator and co-author on the paper, said the study was one of many in which his team has looked at how drugs, especially over-the-counter and prescription medications, impact driving performance.

“What we were really focused on was could we determine whether or not someone was impaired looking at their brain activity,” Brown said.

The team conducted the research at the UI’s National Advanced Driving Simulator in Coralville.

The researchers applied an electroencephalogram, a cap with metal discs that detect brain waves, to the scalps of each person to study their brain responses. The study found frontal midline theta power, which is associated with focused cognitive control and memory encoding, decreased in the subjects who had inhaled marijuana before cognitive and driving tests.

“That’s an area of the brain that’s particularly affected by cannabis, and it’s also being reflected in what’s going on in the performance side of things, operating the vehicle in the roadway,” Brown said.

Chris Berka, CEO and co-founder of Advanced Brain Monitoring, said that other parts of the brain related to memory encoding, not limited to theta power, were specifically suppressed during cannabis ingestion.

“It happens instantly, immediately after inhalation, and it continues all the way into five or six hours, even when people report not starting to feel as intoxicated,” she said. “Theta is very important for memory. It’s important for complex cognitive tasks, but we still don’t fully understand why cannabis is shutting that down, how it’s doing it.”

Berka, co-author on the paper and principal investigator on the project, said researchers used cognitive tasks to test for verbal memory, image recognition memory, and processing speed, all of which are related to driving performance.

The primary measure the researchers used to detect impaired performance, she said, was the standard deviation of lane or the amount a driver swerves in a lane.

“Then they drive for 45 minutes in a simulated driving protocol, where they go through some urban areas and then some long country roads and then we measure the driving performance,” Berka said.

Gary Milavetz, UI College of Pharmacy executive associate dean and co-author on the paper, prepared the doses of cannabis plant material used in the study in addition to analyzing data.

Milavetz said cannabis slows down the speed at which a user drives, unlike alcohol, which does the opposite.

“That’s not necessarily a good thing in that they can become a hazard because they are driving too slow … and block traffic and make it a challenge for people to go around them,” he said.

Cannabis users are slow to react to roadway situations like changing stop lights or moving pedestrians, Milavetz said.

“I think we need a better understanding of the amount of cannabis that caused the impairment, and by that I mean what gets into the bloodstream, because that’s what goes in the brain obviously and affects how people react and respond to driving and most other activities,” he said.

Milavetz said medical marijuana is used to treat anxiety, nausea, and vomiting caused by chemotherapy, among other things.

“People react differently to a dose of THC. Some people seem to get very impaired, some people seem to get sort of moderately impaired and some people have minimal impairment, but it’s still enough to be detectable in our research,” Milavetz said. “That’s why I’m sort of confident in saying there is impairment associated with cannabis, but it’s not necessarily a clear linear relationship.”

Berka said she has worked with the National Advanced Driving Simulator at the UI on many previous studies over the last decade to investigate the effects of drugs and sleep deprivation on driving performance.

“Right now, it’s very difficult for traffic safety and the legal system to keep pace with the rate of legalization, and there’s a great unmet need for better understanding, how does cannabis affect the brain, how do different doses of cannabis affect the brain, and how does that then lead to potential changes in performance,” Berka said.

At the University of Colorado, Berka is involved in a new test in which the subjects use their own legally owned cannabis, as opposed to that issued by the National Institute on Drug Abuse for the UI study.

“That data we think is a step closer to what we would call an in-the-wild study, meaning it’s more representative of the way people are using cannabis in the real world,” she said.