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

Abstract

Individuals at clinical high-risk (CHR) for schizophrenia experience subthreshold symptoms of this disorder, and cannabis use further increases their risk of conversion to psychosis. To seek neurophysiological evidence that cannabis use is associated with semantic processing deficits in the CHR state, we used the N400 event-related potential (ERP) to measure semantic priming. We recorded ERPs in 15 cannabis-using and 12 non-cannabis-using help-seeking CHR individuals, and 10 cannabis-using and 15 non-cannabis-using healthy controls while they viewed related and unrelated prime-target word pairs, at a short and a long stimulus-onset asynchrony (SOA). We observed no significant differences in N400 semantic priming between the four groups, but observed a trend towards deficits at the long SOA in all CHR participants compared to all controls (p = 0.07). The results suggest that CHR individuals experience semantic priming deficits similar to those of schizophrenia patients but that cannabis use does not further impair this process.