Dr Patricia Conrod, Universite de Montreal, studied the year-to-year changes in alcohol and cannabis use and cognitive function in a sample of adolescents consisting of five per cent of all students entering high school in 2012 and 2013.
The students were assessed annually for four years on alcohol and cannabis use, and their cognitive function was evaluated using computerised cognitive tests.
According to the study, 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.
Dr Steven Laviolette team demonstrated that adolescent exposure to tetrahydrocannabinol or THC induces changes in a specific region of the brain called the prefrontal cortex (PFC) and in a brain circuit, the mesolimbic pathway, that closely resemble the abnormalities observed in schizophrenia.
Furthermore, adolescent THC exposure also caused cognitive abnormalities including deficits in social interactions, memory processing and anxiety regulation.
Interestingly, Dr Laviolette's team found that administration of drugs that restore normal PFC function in early adulthood could reverse the effects of adolescent THC exposure.
They also demonstrated that co-administering THC with drugs that prevent the THC-induced disruption in brain signalling pathways prevented the development of schizophrenia-like effects.
Dr Iris Balodis, McMaster University, investigated 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, which explored how much effort an individual is willing to make to receive a given reward.
Participants were given a choice between an easy task or a hard task in which they can gain varying amounts of money. During the administration of this test, Dr Balodis and her team looked at differences in activity in different brain regions by functional magnetic resonance imaging.
Initial findings suggested 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 the activation of specific brain regions known to be important for motivation. This information could be key to finding cannabis addiction vulnerability factors.
Adolescent cannabis use is associated with behavioural changes related to reward and motivation in humans. Paradoxically, this use has both been suggested to increase motivation for other drug use (the gateway hypothesis) and a potential "amotivation syndrome" in which individuals are less willing to expend effort to receive a reward.
Taken together, the research help decipher the links between cannabis use and long-lasting changes in the brain, which underlie changes in behaviour in adolescent humans, and in studies reverse-translating these findings to animal models.