Neurobiological Consequences of Adolescent Cannabis Use
About one in five Canadian adolescents (19% of Canadians aged 15-19) uses cannabis. Its recent legalization across the country warrants investigation into the consequence of this use on the developing brain. Neuroscientists have been researching the effects of cannabis on the adolescent brain. Adolescence is associated with the maturation of cognitive functions, such as working memory, decision-making, impulsivity control and motivation, and the research presented suggests cannabis could have long-lasting effects on these.
Cannabis use and cognitive function
Dr. Patricia Conrod, at Université de Montréal, studied the year-to-year changes in alcohol and cannabis use and cognitive function in a sample of adolescents consisting of 5% of all students entering high school in 2012 and 2013 in the Greater Montreal region (a total of 3,826 7th grade students).
The researchers found substance use to be linked to low cognitive functioning, a finding that could be indicative of an underlying common vulnerability. Cannabis use was linked to impairments in working memory and inhibitory control, which is required for self-control. Cannabis use was also linked to deficits in memory recall and perceptual reasoning.
More recently Dr. Conrod’s team analysed the sex difference in cannabis response in the same sample of adolescents. Preliminary data indicates that cannabis use had a stronger effect on the memory functions of male students than female students. Both sexes were however, equally affected by cannabis on inhibitory control.
THC effect on the adolescent brain
Dr. Steven Laviolette presented research on the effect the primary psychoactive component of cannabis, delta-9-tetrahydrocannabinol or THC, on the adolescent brain, in rodent animal models.
His team demonstrated that adolescent exposure to THC induces changes in the prefrontal cortex (PFC) of the brain and in a brain circuit, the mesolimbic pathway, that closely resemble the abnormalities observed in schizophrenia. Furthermore, adolescent THC exposure also caused affective and cognitive abnormalities including deficits in social interactions, memory processing and anxiety regulation.
Decision making in cannabis users
Dr. Iris Balodis, from McMaster University, investigates the mechanisms that motivate individuals to act and make decisions that can go against a person’s best interest, as seen in people suffering from addiction.
To compare decision-making in individuals suffering from cannabis addiction (also called cannabis use disorder) to healthy controls, Dr. Balodis used an effort-based decision-making test.
Initial findings suggest that there are differences in encoding the value of the reward (money received) and of the effort cost (amount of work done) in individuals addicted to cannabis relative to healthy controls. These were revealed by differences in activation of specific brain regions known to be important for motivation. This information could be key to finding cannabis addiction vulnerability factors.