Emotional speech processing deficits in bipolar disorder : the role of mismatch negativity and P3a

Background: Deficits in emotional prosody processing have been observed in bipolar disorder (BD). While recent neural studies have explored impaired processing of facial expressions, little is known about deficits in emotional speech processing, or the specific stages of processing at which they occur. This study examined if pre-attentive detection and attention to emotional speech is impaired in BD, relative to healthy individuals. Methods: The EEG data was collected from 14 individuals with BD and 14 healthy control (HC) participants while the auditory stimuli was presented via a passive three-stimulus oddball sequence which included emotionally (neutral, happy, sad) spoken syllables and acoustically matched nonvocal tones. Event-related potentials (ERPs) were evaluated in terms of Mismatch Negativity (MMN) and P3a (event-related potentials signals). Results: Individuals with BD showed normal MMN amplitude, but significantly delayed MMN latency and reduced P3a amplitude in response to the emotional syllables compared to HC. Limitations: Small sample size, lack of control of psychopharmacological intervention and no inclusion of an affective prosody-labelling task. Conclusions: The finding that changes in emotional speech prosody in the pre-attentive stages of processing (MMN) were unimpaired in individuals with BD; while automatic orientation towards emotionally salient speech (P3a) was reduced compared to HC, suggests that vocal emotional cues may not be recognised as salient by individuals with BD, resulting in fewer attentional resources allocation to further processing. This may lead to poorer integration of auditory emotional cues and other sensory information and negatively impact interpersonal and psychosocial functions.