Thank you very much for inviting me today. I believe this is a very important endeavour, and I'm happy to be a part of it. I am an associate professor in the school of psychology at the University of Ottawa. I'm a neuro-imager and a neuroscientist.
One avenue of research that I have pursued is how drugs of abuse impact the brain, specifically in youth, during executive functioning. The research I'll be discussing today was funded by the Ontario Research and Development Challenge Fund, ORDCF, and the National Institute on Drug Abuse, NIDA.
This research was performed on a sample of the Ottawa Prenatal Prospective Study participants. OPPS is a study that was started by Dr. Peter Fried at Carleton University in the seventies. It was designed to investigate the impact of prenatal marijuana exposure on children.
There are so many variables that are at play when determining the impact of marijuana on the brain that it's really important to have pre-marijuana measures of the participants. This is what really makes the OPPS population unique in the world, as these participants have been followed and tested every two to three years from the time they were born until they're teenagers and young adults.
There are three other longitudinal studies in the world—in New Zealand, in Pittsburgh, and in Europe—but the OPPS is local, it's Canadian, and it does offer a wealth of information on its participants. Approximately 4,000 lifestyle variables have been collected, including both prenatal drug exposure to marijuana, nicotine, and alcohol, as well as teenage use. The longitudinal nature of the study is really what makes the empirical results so powerful.
As the study went on, Dr. Fried was detecting subtle effects in top-down processing in participants that were exposed prenatally to marijuana and also in those who were starting to use marijuana themselves. He wanted to know more though, so he asked me to perform functional magnetic resonance imaging, fMRI, on them. What is functional MRI? It's a brain imaging technique that allows us to use a regular clinical MRI scanner, but it examines the brain as it works. You're measuring and quantifying blood flow as a person is doing a cognitive task in the scanner.
One of the advantages of fMRI is that it has a level of sensitivity that can uncover differences in brain activity that you wouldn't normally see in just a regular standardized neuropsychological assessment. The tasks that I administer are executive functioning tasks. Executive functioning is an umbrella term for several cognitive processes that consist of decision-making, planning, organizing behaviour, setting a goal and achieving that goal, while inhibiting inappropriate responses and not getting distracted.
We used fMRI during four executive functioning tasks, including working memory, impulsivity, and sustained attention in the OPPS participants when they were between 18 and 21 years of age. We explored both the long-term impact of the prenatal exposure as well as the teenage use of marijuana on brain activity.
To touch briefly on the prenatal exposure findings, one of the most surprising results was that even after 17 years, even more in some of the participants, we were able to detect significant long-term impacts of that prenatal marijuana exposure on the patterns of activity in the brain during executive functioning. We were able to say this confidently because we could control for so many variables due to the longitudinal nature of the OPPS. The more prenatal marijuana the participants were exposed to, the most significant the differences in blood flow.
This is a critical finding given what seems to be the public perception that marijuana has no substantial health risks. It came to my attention recently that some pregnant women are using marijuana for their morning sickness. I was quite surprised at this. Using marijuana for morning sickness may have its short-term positive effects for the mother, but really, the long-term consequences for the child surely outweigh those immediate ones.
I think this is fairly intuitive. We do have empirical evidence, though, and it's mounting, for the adverse effects of marijuana in pregnancy for both the mother and the child.
In addition to the prenatal effects, what I really want to focus on today is the investigation into the teen use of marijuana and its impact on brain activity, brain functioning, during executive functioning.
Where we found our biggest significant results was in response inhibition, or impulsivity. This was a cognitive domain where we detected the most significant effects. Response inhibition allows for successful adaptation to the environment: recognizing unexpected situations, making plans, changing behaviour accordingly. Again, we're comparing our young adults, 18 to 21, from the OPPS, who smoked marijuana regularly. We're looking at them and comparing their brain activity with the brain activity of those who had never smoked marijuana regularly. Regular use was defined as more than one joint per week, and the average consumption was about eleven and a half joints per week.
Despite similar performance among our groups on our response inhibition task, there was a significant difference in brain activity during the task, depending on how much marijuana was smoked. The more marijuana that was smoked, the more brain activity there was, and the more brain regions were recruited to perform the task. These results were most robustly observed in the prefrontal cortex, and this was the same outcome for all the four tasks that we performed. We did working memory and sustained attention, also. More marijuana exposure was related to more widespread brain activity. You might think increased activity is a good thing, but that's not the case. Increased neural activity is actually interpreted as having to work harder, having to engage more brain resources to respond accurately.
This type of demand on the brain is a sign of a required or a necessary compensation. Over time and/or with challenges to that circuitry involved, the brain can't compensate any further. It gets fatigued and it falters. If put into more real-life situations, the marijuana smokers may not be able to adapt or compensate as they can with the easy tasks that we give them to do, and then problems with cognitive efficiency can arise. This is particularly problematic at this time of brain development when the prefrontal cortex is undergoing fine-tuning and optimization for future success. The prefrontal cortex is like the CEO or the band leader of executive functioning. It's really what distinguishes humans from other animals and allows for higher order cognitive functioning that we really rely on for success in the world, whether it's in relationships or in academics, or in professional life.
Our brains are not fully developed until well into adulthood. The development of the brain is actually in high gear during these teenage years. They are key phases of neuronal development that occur before the brain is fully ready to deal with the challenges of the adult world, and these take place specifically in the prefrontal cortex. These include a pruning, whereby neurons that are not being used efficiently get removed, and at the same time, those neurons that are efficient in their communication with other neurons get more shielding, more myelination, and this allows for further efficiency and productivity. This is a time when the brain is being customized, and only with these steps completed are our brains really maximized for success.
Marijuana hijacks this development. When the prefrontal cortex is not fully developed, it is more vulnerable to the neurotoxic effects of marijuana than in adulthood. This is why the age of onset of marijuana use is so critical. These developmental stages are essential, but marijuana exposure gets in the way. Without the cognitive input from a well-developed prefrontal cortex, a teen has to rely on other brain regions for cognition. The limbic system and the more posterior brain regions that are not as evolutionarily developed are what must be relied upon to make decisions and provide judgment. What this means is that our emotional brain is running the show rather than enlisting the help of the thinking brain, or the prefrontal cortex.
Executive functioning is required. To be prosperous in the world without a well-developed prefrontal cortex—something that can happen when it gets hijacked by marijuana—it will be a struggle, and this struggle can be avoided by focusing on brain health.
It's really important, I think, to get these results to the teens and to the parents. My work is published in scientific journals, and who reads those?
We need to educate and inform people that marijuana is not as innocuous as it's being deemed to be, for youth in particular, and that the adolescent developing brain is very vulnerable to the adverse effects of marijuana.
I don't think we can allow the misconceptions of the impact of marijuana on youth to continue. We really do need to have an increased awareness of the neurophysiological effects of marijuana on youth, and I think that's really crucial.