Elevated Mirror Neuron System Activity in Bipolar Mania: Evidence from a Transcranial Magnetic Stimulation Study.

OBJECTIVES: The role of the 'mirror neuron system' (MNS) in the pathophysiology of mood disorders is not well studied. Given its posited role in the often-impaired socio-emotional processes like intention detection, empathy, and imitation, we compared putative MNS-activity in patients with bipolar mania and healthy comparison subjects. We also examined the association between putative MNS-activity and hyper-imitative behaviors in patients.

METHODS: We studied 39 medication-free individuals diagnosed with mania and 45 healthy comparison subjects. TMS-evoked motor cortical reactivity was measured via single and paired-pulse stimuli (assessing SICI - short and LICI - long interval intracortical inhibition) while subjects viewed a static image and goal-directed actions. Manic symptom severity and imitative behaviors were quantified using the Young's Mania Rating Scale and a modification of the Echolalia Questionnaire.

RESULTS: Two-way repeated measures analysis of variance demonstrated a significant group × time interaction effect indicating greater facilitation of cortical reactivity during action observation (putative MNS-activity) in the patient group as compared to the healthy group. While LICI-mediated MNS-activity had a significant association with manic symptom severity (r = 0.35, p = 0.038), SICI-mediated MNS-activity was significantly associated with incidental echolalia scores in a sub-group of 17 patients with incidental echolalia (r = 0.75, p <0.001).

CONCLUSIONS: Our findings demonstrate that putative MNS-activity is heightened in mania, possibly because of disinhibition, and associated with behavioral consequences (incidental echolalia). This article is protected by copyright. All rights reserved.