What you need to know
Adolescents with bipolar disorder have high rates of cannabis use, and when they use cannabis, they tend to have worse symptoms and poor response to treatment. Studies have found abnormal connectivity between reward networks in the brains of people with bipolar disorder. Studies have also found similar problems with connectivity in the brains of people who use cannabis. They found preliminary evidence of cannabis-related differences in functional reward circuits in adolescents with bipolar disorder. The findings may provide insight into the brain basis of the negative clinical consequences associated with cannabis use.
What is this research about?
Adolescents with bipolar disorder have high rates of cannabis use, which previous studies showed increase symptom severity and decrease treatment response. Both bipolar disorder and cannabis use are associated with differences in reward processing. Studies have also found differences in connectivity related to the brain’s reward networks among people with bipolar disorder and among people who use cannabis, both compared to control groups.
Researchers conducted a study to understand brain connectivity related to cannabis use, which ultimately may represent a predisposition to or a consequence of cannabis use, in a sample of adolescents that are particularly vulnerable to cannabis use and its negative effects.
What did the researchers do?
The researchers divided the overall sample of the 134 adolescent participants, ages 13 to 20 years old, into three groups:
- 40 adolescents with bipolar disorder and lifetime cannabis use
- 31 adolescents with bipolar disorder and no history of cannabis use
- 63 healthy controls.
They compared resting state functional connectivity, or in other words, how different brain regions are functionally connected as a circuit, between the three groups. The purpose of the study was to understand the brain connections related to cannabis use, which ultimately may represent a predisposition to or a consequence of cannabis use, in a sample of adolescents that are particularly vulnerable to cannabis use and its negative effects.
The researchers looked at the following brain areas:
- The nucleus accumbens is part of the brain’s reward system and plays an important role in processing and analyzing rewarding and reinforcing information.
- The superior parietal lobe integrates multiple sources of sensory information to form a single perception, and also plays a role in attention processes.
- The orbitofrontal cortex is part of the limbic system and is involved in executive function, in particular, reward-related decision-making.
- The occipital lobe is responsible for visual processing.
This study is the largest to date to examine associations between cannabis use and brain connectivity in adolescents with bipolar disorder and the first such study to include a healthy control group.
What did the researchers find?
The research found significant differences in resting state functional connectivity between the three groups in three specific areas of the brain’s reward network:
- Between the nucleus accumbens and left superior parietal lobe: Adolescents with bipolar disorder who had not previously used cannabis had negative connectivity, while the healthy control group had positive connectivity.
- Between the right orbitofrontal cortex and the right lateral occipital cortex: Adolescents with bipolar disorder who had used cannabis had positive connectivity, while both the healthy control group and the adolescents with bipolar disorder and no history of cannabis use group had negative connectivity.
- Between the right orbitofrontal cortex and right occipital pole: Adolescents with bipolar disorder and lifetime cannabis use had positive connectivity, while adolescents with bipolar disorder and no history of cannabis use had negative connectivity.
According to the researchers, the findings provide insight into how the clinical symptoms associated with cannabis use occur in the brain. They suggest that adolescents with bipolar disorder who use cannabis may find internal reflection (or introspection) less rewarding, which may contribute in part to cannabis use. Adolescents with bipolar disorder who have used cannabis may be predisposed to finding visual cues of cannabis more rewarding. Alternatively, each of these findings may be a consequence of cannabis use, rather than a cause.
Limitations of the research
The researchers noted that the research methods used in this study did not allow them to determine if these connectivity patterns were a result of or the cause of cannabis use. This study also did not include a group of healthy controls with a history of cannabis use. In addition, this study relied on self-reported lifetime cannabis use rather than urine samples, so it’s possible that cannabis use was under reported. They also did evaluate the duration, frequency or potency of the cannabis use so they were not able to assess these areas of interest.
How can you use this research?
This research adds to our understanding of the link between cannabis use and resting state functional connectivity in adolescents with bipolar disorder. It also provides insight into the brain basis for the negative clinical associations of cannabis use. Finally, the research increases our understanding of the brain network patterns that may underlie the predisposition to or a consequence of cannabis use among adolescents with bipolar disorder.
About the researchers
Alysha A. Sultan1,2,3, Megan A. Hird1,3, Mikaela K. Dimick1,2,3, Bradley J. MacIntosh5,6, Benjamin I. Goldstein1,2,3,4,6
- Centre for Youth Bipolar Disorder, Centre for Addiction and Mental Health (Sultan, Hird, Dimick, Goldstein)
- Department of Pharmacology and Toxicology, University of Toronto (Sultan, Dimick, Goldstein)
- Faculty of Medicine, University of Toronto (Sultan, Hird, Dimick, Goldstein)
- Department of Psychiatry, University of Toronto (Goldstein)
- Department of Medical Biophysics, University of Toronto (MacIntosh)
- Hurvitz Brain Sciences Program, Sunnybrook Health Sciences Centre (MacIntosh, Goldstein)