S78. EXAMINING AN EVENT-RELATED BRAIN POTENTIAL INDEX OF SEMANTIC PRIMING IN CANNABIS-USING INDIVIDUALS AT CLINICAL HIGH-RISK FOR PSYCHOSIS

• Published in: Schizophrenia bulletin Vol. 45; no. Supplement_2; p. S337
• Main Authors: Ahmed, Sarah, Lepock, Jennifer R, Maheandiran, Margaret, George, Tony P, Mizrahi, Romina, Kiang, Michael
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 09.04.2019
• Subjects: Poster Session III
• ISSN: 0586-7614; 1745-1701
• DOI: 10.1093/schbul/sbz020.623

Abstract Background Individuals at clinical high-risk (CHR) for schizophrenia experience subthreshold symptoms of this disorder and are at elevated risk for developing it. Among CHR patients as well as the general population, cannabis use has been associated with increased risk of developing psychosis. Psychosis and psychosis-like symptoms in schizophrenia patients, healthy individuals and regular cannabis users have been linked to deficits in processing relationships between meaningful (semantic) stimuli. To seek neurophysiological evidence that semantic processing deficits mediate the relationship between cannabis use and psychosis-like symptoms in the CHR state, we used the electroencephalographic N400 event-related potential (ERP) as a measure of semantic processing. The N400 is seen in response to meaningful stimuli and is smaller when the target stimulus is more related to a preceding prime. We hypothesized that there would be a smaller N400 amplitude difference between target stimuli that are related versus unrelated to a preceding prime stimulus (i.e., smaller semantic priming effects) in cannabis-using compared to non-cannabis-using CHR patients. Methods We recorded ERPs in 12 antipsychotic-naïve CHR patients with history of present or past cannabis dependence disorder, 11 CHR patients with no history of cannabis use and 13 healthy control participants (HCPs). Participants viewed prime words each followed by a target which was either a related or unrelated word, or a nonword, in a lexical-decision task. Equal numbers of each target type were presented at prime-target stimulus-onset asynchronies (SOAs) of 300 and 750 ms. Results Across SOAs, we saw a trend toward N400 semantic priming effects being smaller for both CHR/C+ and CHR/C- compared to controls (p = 0.078). Discussion The results suggest that cannabis use does not modulate semantic priming deficits in CHR patients. A limitation of the study was that some of the cannabis-dependent CHR group were in remission. Future studies of CHR patients comparing those who have current cannabis dependence with non-users might detect differences between these groups.