1. Cannabis use in early adolescence: Evidence of amygdala hypersensitivity to signals of threat
Author: Spechler et al. Presenters: Richard Groves and Iman Qubtan Word count: 398
Background
Neurodevelopment of the amygdala in adolescence is linked with
temporary changes in emotional processing. Both early cannabis
use and increased amygdala activity are associated with an
increased risk of mood disorders (e.g. depression). Given the high
density of cannabinoid receptors in these brain areas, and
changing societal attitudes to cannabis, it is important to study the
impact of cannabis consumption during this period of change.
Previous research shows that cannabis intake reduces amygdala
activity in adults in response to angry faces (Gruber et al., 2009).
However, due to lack of research, it is uncertain whether these
results generalise to adolescents.
AIM: Use fMRI scans to compare cannabis using adolescents with
matched controls in their brain response to videos of neutral and
angry faces.
Methods
PARTICIPANTS: 14 years old; 70 cannabis users (mostly low-level
use) and 70 controls matched on sex, IQ, handedness,
socioeconomic status, and other drug use.
TASK: fMRI scans were obtained whilst participants watched short
videos of faces or a control picture (concentric circles).
Two facial emotion conditions:
1. Neutral expression to different neutral expression.
2. Neutral expression to angry expression.
Results
• Greater activity in right and left amygdalae in cannabis users
viewing angry faces compared to neutral faces.
• Controls showed no such differences.
• Greater activity in the right temporal parietal junction (TPJ) in
controls viewing neutral faces compared to angry faces.
• Cannabis users showed no such differences.
Conclusion
• Contrary to adult research, adolescent cannabis users showed
amygdala hypersensitivity to angry emotions.
• Brain developments may make adolescents particularly sensitive
to cannabis.
• Cannabis use may cause brain changes that put adolescents at
risk of mood disorders.
• Right TPJ associated with social cognition.
• Neutral faces more ambiguous so required more cognitive
resources.
• Lack of effect of face emotion on TPJ activity in cannabis users
may indicate general deficits in social processing.
Discussion
STRENGTHS:
• Large and matched samples controlled for confounding variables.
• FMRI provided adequate temporal and spatial resolutions for
facial emotion to be linked with activity in specific brain areas.
WEAKNESSES:
• Cross-sectional study so cannot infer causation; initial brain
differences may cause certain adolescents to experiment with
cannabis.
• Uncertain that large brain differences can emerge from low-level
cannabis use.
FUTURE DIRECTIONS:
• Longitudinal studies should measure brain activity before
cannabis use so causation can be inferred.
• Extend research to older cannabis users with a variety of
consumption frequencies.
• Look at the effect of cannabis on the endogenous cannabinoid
system at the neuronal level.
Figure 2. Mean activation for face type by group plotted for left and right amygdala.
Figure 1. The facial emotion and control stimuli. Videos were 2-5 s long and were
presented in black and white.
Figure 3. Mean activation for face type by group plotted for the brain cluster
spanning the right temporal parietal junction.
References
Gruber, S. A., Rogowska, J., & Yurgelun-Todd, D. A. (2009). Altered
affective response in marijuana smokers: An FMRI study. Drug and Alcohol
Dependence, 105 (1), 139-153.
Spechler, P. A., Orr, C. A., Chaarani, B., Kan, K., Mackey, S., Morton, A., …
& the IMAGEN Consortium (2015). Cannabis use in early adolescence:
Evidence of amygdala hypersensitivity to signals of threat. Developmental
Cognitive Neuroscience, 16, 63-70.