Weed or Wheel! fMRI, Behavioural, and Toxicological Investigations of How Cannabis Smoking Affects Skills Necessary for Driving

Abstract

Marijuana is the most widely used illicit drug, however its effects on cognitive functions underling safe driving remain mostly unexplored. Our goal was to evaluate the impact of cannabis on the driving ability of occasional smokers, by investigating changes in the brain network involved in a tracking task. The subject characteristics, the percentage of Δ9-Tetrahydrocannabinol in the joint, and the inhaled dose were in accordance with real-life conditions. Thirty-one male volunteers were enrolled in this study that includes clinical and toxicological aspects together with functional magnetic resonance imaging of the brain and measurements of psychomotor skills. The fMRI paradigm was based on a visuo-motor tracking task, alternating active tracking blocks with passive tracking viewing and rest condition. We show that cannabis smoking, even at low Δ9-Tetrahydrocannabinol blood concentrations, decreases psychomotor skills and alters the activity of the brain networks involved in cognition. The relative decrease of Blood Oxygen Level Dependent response (BOLD) after cannabis smoking in the anterior insula, dorsomedial thalamus, and striatum compared to placebo smoking suggests an alteration of the network involved in saliency detection. In addition, the decrease of BOLD response in the right superior parietal cortex and in the dorsolateral prefrontal cortex indicates the involvement of the Control Executive network known to operate once the saliencies are identified. Furthermore, cannabis increases activity in the rostral anterior cingulate cortex and ventromedial prefrontal cortices, suggesting an increase in self-oriented mental activity. Subjects are more attracted by intrapersonal stimuli (“self”) and fail to attend to task performance, leading to an insufficient allocation of task-oriented resources and to sub-optimal performance. These effects correlate with the subjective feeling of confusion rather than with the blood level of Δ9-Tetrahydrocannabinol. These findings bolster the zero-tolerance policy adopted in several countries that prohibits the presence of any amount of drugs in blood while driving.

Comparison of cannabinoid concentrations in oral fluid and whole blood between occasional and regular cannabis smokers prior to and after smoking a cannabis joint

“…The weakened feeling of confusion among heavy smokers reflects a greater tolerance to negative symptoms. These effects as felt by occasional smokers are discussed in depth by Battistella et al [26]. Similar effects involving a tolerance mechanism have been found by others and are presented in a recent paper of Theunissen et al [44].…”

“…The overall design of the study has been described in a previous publication and its supportive information [26]. The study was expanded in order to include regular cannabis smokers.…”

THCCOOH concentrations in whole blood: Are they useful in discriminating occasional from heavy smokers?

“…[15] The imaging sessions determined the timeframe of the one-day experiment. The study was extended to include a similar-sized group of young male heavy cannabis smokers.…”

Development of a rapid column-switching LC-MS/MS method for the quantification of THCCOOH and THCCOOH-glucuronide in whole blood for assessing cannabis consumption frequency

“…Not surprisingly, roadside surveys have demonstrated that driving under the influence of cannabis (DUIC) is a common and widespread occurrence [2][3][4][5]. Cannabis consumption has been shown to have impairing effects on cognitive functions and psychomotor skills related to driving and to be associated with an elevated accident risk [6][7][8][9]. Thus, DUIC has severe implications on global road safety and is considered a serious criminal offense in many countries [10].…”