4. Bhattacharyya S, Wilson R, Appiah-Kusi E, et al. Effect of cannabidiol on medial temporal, midbrain, and striatal dysfunction in people at clinical high risk of psychosis: a randomized clinical trial. JAMA Psychiatry. 2018;75(11):1107-1117.
Current preclinical models suggest that psychosis involves a disturbance of activity in the medial temporal lobe (MTL) that drives dopamine dysfunction in the striatum and midbrain. THC, which produces psychotomimetic effects, impacts the function of the striatum (verbal memoryand salience processing) andamygdala (emotional processing), and alters the functional connectivity of these regions. Compared with THC, CBD has broadly opposite neural and behavioral effects, including opposing effects on the activation of these regions. Bhattacharyya et al7 examined the neurocognitive mechanisms that underlie the therapeutic effects of CBD in psychosis and sought to understand whether CBD would attenuate functional abnormalities in the MTL, midbrain, and striatum.
Study design
- A randomized, double-blind, placebo-controlled trial examined 33 antipsychotic-naïve participants at clinical high risk (CHR) for psychosis and 19 healthy controls. The CHR group was randomized to CBD, 600 mg, or placebo.
- Three hours after taking CBD or placebo, CHR participants were studied using fMRI while performing a VPA learning task, which engages verbal learning and recall in the MTL, midbrain and striatum. Control participants did not receive any medication but underwent fMRI while performing the VPA task.
- The VPA task presented word pairs visually, and the accuracy of responses was recorded online. It was comprised of 3 conditions: encoding, recall, and baseline.
Outcomes
- Brain activation was analyzed in 15 participants in the CBD group, 16 in the placebo group, and 19 in the control group. Activation during encoding was observed in the striatum (specifically, the right caudate). Activation during recall was observed in the midbrain and the MTL (specifically, the parahippocampus).
- Brain activation levels in all 3 regions were lowest in the placebo group, intermediate in the CBD group, and greatest in the healthy control group. For all participants, the total recall score was directly correlated with the activation level in the left MTL (parahippocampus) during recall.
Conclusion
- Relative to controls, CHR participants exhibited different levels of activation in several regions, including the 3 areas thought to be critical to the pathophysiology of psychosis: the striatum during verbal encoding, and the MTL and midbrain during verbal recall.
- Compared with those who received placebo, CHR participants who received CBD before completing the VPA task demonstrated greater levels of brain activation and higher recall score.
- These findings suggest that CBD may partially normalize alterations in MTL, striatal, and midbrain function associated with CHR of psychosis. Because these regions are implicated in the pathophysiology of psychosis, the impact of CBD at these sites may contribute to the therapeutic effects of CBD that have been reported by some patients with psychosis.
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