Rationale Cannabis use is prevalent among the early psychosis (EP) population. The event-related potentials, mismatch negativity (MMN) and P3a are reduced in EP. Cannabinoids have been shown to modulate N-methyl-Daspartate receptors which are involved in MMN generation. Objectives This study is the first to investigate the effects of cannabis use on MMN/P3a in EP. Methods EP was defined as a history of psychosis or psychotic symptoms with no progression to date to chronic schizophrenia. Twenty-two EP patients with cannabis use (EP+CANN), 22 non-cannabis-using EP patients (EPCANN) and 21 healthy controls participated in this study. MMN/P3a was elicited using a two-tone, auditory paradigm with 8% duration deviants. Results As expected, EP-CANN showed marked reductions in MMN/P3a amplitudes compared to controls. However, EP+CANN showed evidence of a different pattern of neurophysiological expression of MMN/P3a compared to nonusing patients, most notably in terms of delayed frontal MMN/P3a latencies. Conclusions This study provides further evidence that MMN/P3a deficits are present during early psychosis and suggests that this biomarker may have utility in differentiating substance- from non-substance-related psychoses.
- Mismatch negativity