title: Reduced mu suppression and altered motor resonance in euthymic bipolar disorder: Evidence for a dysfunctional mirror system?
abstract: Social cognitive difficulties are common in the acute phase of bipolar disorder and, to a lesser extent, during the euthymic stage, and imaging studies of social cognition in euthymic bipolar disorder have implicated mirror system brain regions. This study aimed to use a novel multimodal approach (i.e., including both transcranial magnetic stimulation (TMS) and electroencephalogram (EEG)) to investigate mirror systems in bipolar disorder. Fifteen individuals with euthymic bipolar disorder and 16 healthy controls participated in this study. Single-pulse TMS was applied to the optimal site in the primary motor cortex (M1), which stimulates the muscle of interest during the observation of hand movements (goal-directed or interacting) designed to elicit mirror system activity. Single EEG electrodes (C3, CZ, C4) recorded mu rhythm modulation concurrently. Results revealed that the patient group showed significantly less mu suppression compared to healthy controls. Surprisingly, motor resonance was not significantly different overall between groups; however, bipolar disorder participants showed a pattern of reduced reactivity on some conditions. Although preliminary, this study indicates a potential mirror system deficit in euthymic bipolar disorder, which may contribute to the pathophysiology of the disorder.
authors.affiliation: a School of Psychological Sciences , Monash University , Clayton , VIC , Australia.|b Monash Alfred Psychiatry Research Centre, The Alfred and Central Clinical School , Monash University , Melbourne, VIC , Australia.
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Andrews
authors.affiliation: b Monash Alfred Psychiatry Research Centre, The Alfred and Central Clinical School , Monash University , Melbourne, VIC , Australia.|c Cognitive Neuroscience Unit, School of Psychology , Deakin University , Burwood , VIC , Australia.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Enticott
authors.affiliation: b Monash Alfred Psychiatry Research Centre, The Alfred and Central Clinical School , Monash University , Melbourne, VIC , Australia.
authors.forename: Kate E
authors.initials: KE
authors.lastname: Hoy
authors.affiliation: b Monash Alfred Psychiatry Research Centre, The Alfred and Central Clinical School , Monash University , Melbourne, VIC , Australia.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Thomson
authors.affiliation: b Monash Alfred Psychiatry Research Centre, The Alfred and Central Clinical School , Monash University , Melbourne, VIC , Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
mesh_terms: D000328:Adult; D000368:Aged; D001714:Bipolar Disorder / Q000503:physiopathology*; D058256:Brain Waves; D003071:Cognition; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D011930:Reaction Time; D012938:Social Perception; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult
keywords: Electroencephalogram; Mirror neurons; Social cognition; Theory of mind; Transcranial magnetic stimulation