Impairments in "top-down" processing in bipolar disorder: a simultaneous fMRI-GSR study.

Understanding the underlying neurobiology of bipolar disorder especially in the euthymic state is essential to furthering our understanding of pertinent psychiatric questions involving the observed symptomatology of the illness. In this study we investigated the mechanisms that underpin the modulation of affect in bipolar disorder to examine the contributions of cortico-limbic brain networks in the processing of affect. We employed a simultaneous functional magnetic resonance imaging and galvanic skin response methodology to investigate top-down networks in euthymic bipolar patients and healthy controls. Galvanic skin responsivity was used to partition neural epochs in which arousal pertaining to the appreciation of disgust stimuli was processed. The results of this study demonstrate that patients with bipolar disorder exhibited impairments in the recruitment of top-down brain networks and as such were unable to engage, to the same extent as matched controls, essential prefrontal processing needed to evaluate emotional salience. Partitioning top-down networks on the basis of arousal measures provided a context within which the modulation of brain networks specialised for the processing of emotion, as well as their interplay with other brain regions including the frontal lobes, could be studied.