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

Area of Science:

• Neuroscience
• Cognitive Psychology
• Psychiatry

Background:

• Bipolar disorder (BD) and schizophrenia (SZ) share language and thought impairments, likely stemming from semantic memory deficits.
• Event-related potentials (ERPs) offer a window into the neural underpinnings of semantic processing.

Purpose of the Study:

• To investigate the nature of semantic processing in BD and SZ.
• To explore differences in how patients with BD and SZ resolve semantic ambiguity.
• To utilize ERPs, specifically the N400 component, as a neurophysiological marker.

Main Methods:

• EEG recording was performed on 12 BD patients, 10 SZ patients, and 21 healthy controls (HC).
• Participants completed a semantic ambiguity resolution task involving sentences with homophones and targets.
• The N400 amplitude was analyzed in response to congruent and incongruent targets in ambiguous and unambiguous conditions.

Main Results:

• Significant differences in N400 amplitude were observed between groups when processing homophones.
• Schizophrenia patients made more semantic resolution errors and showed a larger N400 congruity effect in ambiguous conditions compared to BD patients.
• Bipolar disorder patients exhibited an opposite N400 congruity effect in ambiguous conditions, suggesting difficulty inhibiting dominant meanings.

Conclusions:

• Semantic processing differs significantly between bipolar disorder and schizophrenia.
• Patients with SZ struggle with contextual integration, while BD patients show difficulties in inhibiting dominant homophone meanings.
• Further research with larger cohorts is necessary to establish reliable neurophysiological markers for BD and SZ.