MMN/P3a deficits in first episode psychosis: comparing schizophrenia-spectrum and affective-spectrum subgroups.

BACKGROUND: Reduced mismatch negativity (MMN) and P3a amplitudes are neurophysiological biomarkers for schizophrenia that index deviance detection and the orienting response, respectively. First-episode psychosis (FEP) patients show reduced amplitudes of the 'MMN/P3a complex', but it is unclear whether this occurs across the FEP spectrum.
METHODS: Fifty-three young people (17-36 years) were assessed: 17 FEP affective-spectrum (bipolar disorder with psychotic features and major depressive disorder with psychotic features), 18 FEP schizophrenia-spectrum (schizophrenia, schizoaffective disorder, and schizophreniform disorder), and 18 healthy controls. MMN/P3a was acquired during a two-tone, auditory paradigm with 8% duration deviants. Clinical, psychosocial and neuropsychological assessments were also undertaken.
RESULTS: FEP schizophrenia- and FEP affective-spectrum showed significantly reduced fronto-central MMN and central P3a amplitudes compared to controls. FEP subgroups also showed significantly poorer cognitive and psychosocial functioning. The combined FEP sample showed significant correlations between fronto-central MMN amplitudes and cognitive measures. DISCUSSION: FEP schizophrenia-spectrum and FEP affective-spectrum were similarly impaired in two biomarkers for schizophrenia. FEP subgroups showed impairments in fronto-central MMN consistent with chronic patients. Similarly, both subgroups showed reductions in P3a; although the affective subgroup showed an 'intermediate' frontal response. These findings suggest that FEP patients with both affective and schizophrenia spectrum diagnoses share common neurobiological disturbances in deviance detection/orienting processes in the early phase of illness.