Atypical right hemispheric functioning in the euthymic state of bipolar affective disorder

Bipolar disorder (BD) has been associated with right hemisphere dysfunction. These findings usually come from studies that have not distinguished between symptomatic and euthymic states of BD. The present study aims to investigate atypical right (and left) hemispheric functioning in euthymic BD patients. We evaluated 40 participants (18 healthy controls and 22 euthymic BD patients) using an emotional prosody dichotic listening task and a linguistic dichotic listening task which have been shown to produce a strong left ear advantage (LEA) and right ear advantage (REA), indicating a right and left hemisphere superiority, respectively. The results replicate the well-known LEA in emotional prosody for healthy controls. In contrast, no ear advantage was found for emotional prosody in euthymic BD patients. Both groups revealed the well-established REA in the linguistic dichotic listening task. The patient group was heterogeneous with regard to medication, as it consisted of patients with a variety of pharmacological treatments. The results are in line with previous studies in symptomatic BD patients, and suggest that atypical LEA in emotional prosody can be interpreted as a neurobehavioral vulnerability marker of emotional dysregulation and dysfunction in the right hemispheric fronto-temporal network in both symptomatic and euthymic BD patients.