Alterations of complex mismatch negativity (cMMN) elicited by a two-tone pattern paradigm in early-phase psychosis

The mismatch negativity (MMN) is a component of the event-related potential (ERP) elicited by a change in auditory stimulation (e.g., the occurrence of a deviant sound that violates the rules or regularities of the preceding stimulus sequence) regardless of whether one is attending to the change or not. As such, the MMN provides a useful index of pre-attentive cognition. While decreases in MMN amplitude are robustly observed in chronic schizophrenia, these deficits are less consistently present at the early phase of the illness. The current study utilizes a two-tone pattern paradigm that requires more complex computations than typical oddball stimulus presentations, which may be more appropriate for elucidating MMN deficits in an early phase psychosis (EP) sample. The stimuli were a standard sequence consisting of two alternating tones with different tonal frequencies (eg. ABABAB…), with MMN-eliciting pattern violations created by repetitions of either the A or the B tone. EEG recordings of 15 EP participants and 12 healthy controls (HCs) were collected. While no between-group differences were observed, MMN amplitudes in the EP group were correlated with positive and negative psychosis symptom scores. Follow-up analysis stratifying EP participants according to illness duration showed a reduced MMN amplitude in EP participants with a longer (2+ years) duration of illness, but not in EP participants who were within the first year of illness. These findings suggest a two-tone pattern paradigm may be useful in characterizing MMN-indexed cortical impairment later in the early phase of the illness, but not at first episode.