A recent study published in the Journal of Psychopharmacology has found that cannabis use is associated with alterations in the connectivity of a specific brain network called the executive control network. However, these alterations do not seem to differ significantly between adolescent and adult cannabis users, challenging the expectation that adolescents might be more affected by the substance in this particular brain network.
“Cannabis use is common among adults and adolescence and there is a lot of conflicting information about the relative harms and safety of regular cannabis use,” explained study author Natalie Ertl, a clinical imaging research scientist at Invicro and PhD student at Imperial College London. “Particularly among adolescent users, where the endocannabinoid system is undergoing rapid maturation, we were interested in uncovering how regular cannabis use may disproportionately interfere with brain networks in this group. Resting-state networks are an excellent way to look at many networks in the brain all in one go.”
Resting-state functional magnetic resonance imaging (rs-fMRI) is a common method used to study brain function. Resting-state networks (RSNs) are groups of brain regions that exhibit synchronized activity even when an individual is not engaged in a specific task.
The researchers aimed to determine if there are differences in RSN connectivity between individuals who regularly use cannabis and those who do not (controls). Previous research had shown mixed findings on the effects of cannabis on brain function, and this study aimed to provide more clarity in the context of specific RSNs, such as the default mode network, the executive control network, and the salience network, along with three striatal networks and the hippocampal network.
For their study, Ertl and her colleagues conducted a cross-sectional analysis of rs-fMRI data collected as part of the “CannTeen” study. The participants underwent an MRI session that included an 8-minute resting-state scan.
The study included a total of 140 participants, equally divided into four groups: adolescent cannabis users, adult cannabis users, adolescent non-using controls, and adult non-using controls. The participants were recruited from the Greater London area through various means, including school assemblies, posters, and online advertisements. Detailed demographic and questionnaire data were collected from the participants, including information on drug history, risk-taking behavior, and depression symptoms.
The researchers found that adolescents generally showed lower connectivity compared to adults, except for the salience network, where adolescents had relatively higher connectivity. However no significant interaction effects were found between age group and cannabis use status. This indicates that the relationship between regular cannabis use and resting-state network functional connectivity is not different in adolescents and adults.
“We had hypothesised that the adolescent group would be different to the adult group, as the endocannabinoid system is very different in teenagers,” Ertl told PsyPost. “We were unsure whether the difference would prove protective or make adolescent users more vulnerable, so we were very surprised to find there was no difference between the two age groups.”
But the researchers observed differences in connectivity within the executive control network, where cannabis users exhibited greater connectivity compared to controls. This may reflect compensatory mechanisms or functional alterations due to cannabis use. These differences in connectivity were localized to regions including the dorsal anterior cingulate cortex, motor cortex, middle and posterior insula, temporo-parietal junction, and superior temporal gyrus.
“Another (sort of) surprise was finding a difference in the executive control network (which is involved in attention and high-level task performance) since this was a resting-state scan, so the participants were lying down and resting, not doing anything,” Ertl explained. “The network which is most active at rest is default mode network, so we were maybe expecting to see a difference in that network.”
No consistent differences associated with cannabis use were found in the other networks tested (default mode network, salience network, hippocampal network, and striatal networks). There were also no significant correlations between cannabis use frequency and network connectivity, highlighting that the relationship between cannabis use and brain connectivity is complex and may not be solely determined by frequency of use.
Overall, the findings provide evidence “that regular cannabis may affect brain systems involved in attention, and high-level task performance, but that effects on teenagers don’t seem to be different to adults,” Ertl told PsyPost.
The study provides valuable insights into the relationship between cannabis use and resting-state functional connectivity in the brain. However, the complexity of the brain and the variability of individual responses to cannabis use mean that more research is needed to fully understand the impact of cannabis on brain networks.
“A problem with cross-sectional data is that, while we attempted to match the participants as well as we could, there will always be differences between two groups which cannot be controlled for and therefore cross-sectional data shows a relationship but not causality,” Ertl explained. In addition, “our group of users were considered regular cannabis users but not heavy users, so perhaps our findings cannot be generalized to problem users.”
“Although our data showed (at least in resting state networks) cannabis is not more harmful to teenagers, cannabis is more easily accessible to teenagers than alcohol as dealers are under no obligation to check ID,” Ertl added. “Prohibition makes smoking weed as a youngster much easier!”
The study, “Associations between regular cannabis use and brain resting-state functional connectivity in adolescents and adults“, was authored by Natalie Ertl, Will Lawn, Claire Mokrysz, Tom P. Freeman, Naji Alnagger, Anna Borissova, Natalia Fernandez-Vinson, Rachel Lees, Shelan Ofori, Kat Petrilli, Katie Trinci, Essi Viding, H. Valerie Curran, and Matthew B. Wall.