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
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.