No association between symptom severity and MMN impairment in schizophrenia: A meta-analytic approach

The mismatch negativity (MMN) is an event-related potential that is consistently attenuated in people with schizophrenia. Within the predictive coding model of psychosis, MMN impairment is thought to reflect the same prediction failures that are also thought to underlie the development and crystallization of delusions and hallucinations. However, the true relationship between symptom severity and MMN impairment across studies has not yet been established. The present meta-analysis used meta-regressions to examine the relationship between MMN impairment (quantified as Hedges' g) and PANSS positive and negative symptom totals across 62 and 68 samples, respectively. Furthermore, we examined the relationship between MMN impairment and group differences in educational achievement (n = 47 samples), cognitive ability (n = 36 samples), and age (n = 86 samples). Overall, we found no significant associations between MMN impairment and symptom severity (p's > 0.50); however, we did observe a trend-level association between MMN impairment and lower education (p = 0.07) and a significant association with older age (p < 0.01) in the schizophrenia patient group. Taken together, these results challenge a simple predictive coding model of psychosis, and suggest that MMN impairment may be more closely associated with premorbid functioning than with the expression of psychotic symptoms.