UBC Theses and Dissertations
Phenomenological markers of future psychosis : the role of cannabis Brooks, Gabriel
Cannabis use is a known risk factor for the development of psychosis, although the precise nature of this relationship is unclear. The phenomenological experiences associated with cannabis use vary dramatically, and for some resemble certain features of psychosis. We hypothesized that individuals who report particularly unusual experiences associated with cannabis use demonstrate similar electrophysiological patterns to those who score high on schizotypal personality traits. The Cannabis Experiences Questionnaire (CEQ) and the Schizotypal Personality Questionnaire (SPQ) were used to measure these experiences and traits. A sample of 97 individuals were placed into one of five groups: high CEQ scorers (High CEQ), high SPQ scorers (High SPQ), high CEQ and SPQ scorers (High on Both), average CEQ and SPQ scorers (Average Users), and average SPQ non-users (Average Non-Users). Participants completed a visual task in which they indicated whether they saw a face embedded within a static field. Electroencephalography was used to measure the neural response to the stimuli. The N170 event-related potential (ERP) was used to measure perceptual encoding of the stimulus. The High SPQ and High on Both groups elicited significantly reduced N170 ERPs compared to the average groups. The High CEQ group demonstrated significantly reduced N170 ERPs compared to Average Non-Users. None of the high scoring groups significantly differed in N170 ERP response from each other. No interaction was detected between trial-type and group, although group differences in laterality were robust and consistent across trial types. Replicating past research, the CEQ and SPQ scales moderately correlated with each other. We propose that the detected attenuated N170 ERP demonstrated by the high scoring groups is a manifestation of an underlying shared cognitive vulnerability.
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