The effects of regular cannabis use on cognition, brain volume and chemistry

: A multimodal approach

Abstract

Cannabis is the most widely used recreational drug globally. There is still uncertainty and a lack of consensus with regards to the effects of cannabis on cognition, brain structure and neurological function. An issue with a majority of the existing literature is the failure to match experimental groups and control groups for tobacco use. A large amount focuses on heavy cannabis users, which may not be representative of more recreational cannabis users who only smoke a few times a week.
The aim of this thesis was to use a comprehensive approach to investigate the effects of regular cannabis use on cognition, brain structure, and brain chemistry in a group of relatively young recreational cannabis users. The association between cannabis exposure, cognitive deficits associated with its use, and their neural correlates remain unclear necessitating further exploration. These were assessed using voxel-based morphometry, Magnetic-Resonance-Spectroscopy and neuropsychological assessment tools. Cannabis users were compared on these measures to tobacco smokers and drug naïve controls. A further aim was to assess the relationship between the amount of cannabis and cigarette exposure and the aforementioned measures.
Compared to tobacco smokers there were no significant differences in memory performance in the cannabis users. There were also no significant difference in general IQ scores between any of the groups. Despite no difference in neuropsychological performance, Magnetic-Resonance-Imaging and voxel-based morphometry revealed lower grey matter volumes in the brains frontal lobe, and grey matter increases in a number of regions including the putamen, motor cortex and thalamus in the cannabis users and the tobacco smokers compared to the non smoking controls. Additionally, significant reductions in prefrontal glutamate were observed in the cannabis users and tobacco smokers compared to non-smokers. There were no differences between the cannabis users and the tobacco smokers in either grey matter volume or neurochemistry and the relationship between brain volume and glutamate levels did not differ across groups.
Findings suggest that a some of the structural and neurochemical changes associated with cannabis use reported in the literature may be linked with tobacco use.

Date of Award	10 Jun 2021
Original language	English
Awarding Institution	University of Roehampton
Supervisor	Paul Allen (Director of Studies), Paul Faulkner (Co-Supervisor) & Kaz Brandt (Co-Supervisor)