Running title: ‘cannabis and musical reward’
Abstract
Reward processing can be parsed into dissociable components of anticipation (e.g. wanting) and consummation (e.g. liking). Dysfunctional reward anticipation is a transdiagnostic pathology spanning depression, schizophrenia and addiction. The rewarding effects of cannabis may be caused by its primary psychoactive constituent, delta-9-tetrahydrocannabinol (THC). Cannabidiol (CBD) is another cannabis constituent that can inhibit some effects of THC. This study had the following objectives: 1) to investigate the acute effects of cannabis on reward anticipation and consummation, 2) to establish whether these effects are blocked by CBD.
Across 3 sessions, 16 healthy cannabis users inhaled vaporized cannabis preparations containing 8mg THC, 8mg THC + 10mg CBD, and placebo. Reward consummation was indexed using functional Magnetic Resonance Imaging, evidenced by greater signal whilst listening to classical music versus scrambled sound. Regions of interest were selected from a meta-analysis of music-evoked emotion, and all results were False Discovery Rate corrected. Reward anticipation was recorded using the visual analogue scale ‘want to listen to music’; post-hoc tests were Bonferroni-corrected.
Analysis of consummatory reward showed that cannabis containing THC only reduced activation in bilateral temporal gyrus (right: p=0.005, left: p=0.008), right hippocampus (p=0.025), right amygdala (p=0.025), right insula (p=0.026) and right medial orbitofrontal cortex (OFC, p=0.033). Cannabis containing THC and CBD did not alter signal in any regions. Across all scans, OFC activation correlated with subjective pleasure ratings (r(48)=0.463, p<0.001). Both types of cannabis increased reward anticipation to a similar extent (THC: p=0.001, THC+CBD: p=0.006).
Reward anticipation is primed by cannabis, regardless of its CBD content. By contrast, cannabis reduces neural activation to reward consummation, and this effect is blocked by CBD. These dissociable effects support a role of the endocannabinoid system in reward dysfunction seen in depression, schizophrenia and addiction.