Differential semantic processing in patients with schizophrenia versus bipolar disorder: an N400 study

Abstract

Objective: Both bipolar disorder (BD) and schizophrenia (SZ) are associated with language and thought symptoms that probably reflect a semantic memory-related impairment. We conducted a preliminary study to explore the nature of semantic processing in these disorders, using event-related potentials (ERPs).

Methods: Twelve patients with BD, 10 patients with SZ and a matched group of 21 healthy controls (HC) underwent EEG recording while they heard sentences containing homophones or control words and performed a semantic ambiguity resolution task on congruent or incongruent targets.

Results: Mean N400 amplitude differed between groups for homophones. Patients with SZ made more resolution errors than HC and exhibited a greater N400 congruity effect in ambiguous conditions than BD. In BD, the opposite N400 congruity effect was observed in ambiguous conditions.

Conclusion: Results indicated differences in semantic processing between BD and SZ. Further studies with larger populations are needed in order to develop neurophysiological markers of these disorders.

Significant outcomes: In ambiguous conditions, patients with SZ exhibited a greater N400 difference between congruent and incongruent conditions than patients with BD.In ambiguous conditions, patients with SZ exhibited greater N400 amplitude in incongruent conditions than in congruent ones, whereas patients with BD exhibited the opposite N400 congruity effect.Ambiguity resolution results suggest that patients with SZ have difficulty considering the context, while patients with BD overactivate the dominant meaning of homophones and have difficulty inhibiting it.

Keywords: N400; bipolar disorder; schizophrenia; semantics.