title: Is the human mirror neuron system plastic? Evidence from a transcranial magnetic stimulation study.
abstract: Virtual lesions in the mirror neuron network using inhibitory low-frequency (1Hz) transcranial magnetic stimulation (TMS) have been employed to understand its spatio-functional properties. However, no studies have examined the influence of neuro-enhancement by using excitatory high-frequency (20Hz) repetitive transcranial magnetic stimulation (HF-rTMS) on these networks. We used three forms of TMS stimulation (HF-rTMS, single and paired pulse) to investigate whether the mirror neuron system facilitates the motor system during goal-directed action observation relative to inanimate motion (motor resonance), a marker of putative mirror neuron activity. 31 healthy individuals were randomized to receive single-sessions of true or sham HF-rTMS delivered to the left inferior frontal gyrus - a component of the human mirror system. Motor resonance was assessed before and after HF-rTMS using three TMS cortical reactivity paradigms: (a) 120% of resting motor threshold (RMT), (b) stimulus intensity set to evoke motor evoked potential of 1-millivolt amplitude (SI1mV) and (c) a short latency paired pulse paradigm. Two-way RMANOVA showed a significant group (true versus sham) X occasion (pre- and post-HF-rTMS motor resonance) interaction effect for SI1mV [F(df)=6.26 (1, 29), p=0.018] and 120% RMT stimuli [F(df)=7.01 (1, 29), p=0.013] indicating greater enhancement of motor resonance in the true HF-rTMS group than the sham-group. This suggests that HF-rTMS could adaptively modulate properties of the mirror neuron system. This neuro-enhancement effect is a preliminary step that can open translational avenues for novel brain stimulation therapeutics targeting social-cognition deficits in schizophrenia and autism.
authors.affiliation: Department of Psychiatry, National Institute of Mental Health & Neurosciences (NIMHANS), Bangalore 560029, India. Electronic address: Urvakhsh@gmail.com.
authors.forename: Urvakhsh Meherwan
authors.initials: UM
authors.lastname: Mehta
authors.affiliation: Department of Psychiatry, Smt. Kashibai Navale Medical College and Genral Hospital, Pune 411041, India.
authors.forename: Avinash V
authors.initials: AV
authors.lastname: Waghmare
authors.affiliation: Department of Psychiatry, National Institute of Mental Health & Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Jagadisha
authors.initials: J
authors.lastname: Thirthalli
authors.affiliation: Department of Psychiatry, National Institute of Mental Health & Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Ganesan
authors.initials: G
authors.lastname: Venkatasubramanian
authors.affiliation: Department of Psychiatry, National Institute of Mental Health & Neurosciences (NIMHANS), Bangalore 560029, India.
authors.forename: Bangalore N
authors.initials: BN
authors.lastname: Gangadhar
mesh_terms: D000328:Adult; D001321:Autistic Disorder / Q000175:diagnosis / Q000503:physiopathology; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D059167:Mirror Neurons / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D012559:Schizophrenia / Q000175:diagnosis / Q000503:physiopathology; D013647:Task Performance and Analysis; D050781:Transcranial Magnetic Stimulation / Q000379:methods
keywords: Broca's area; Mirror neurons; Social cognition; TMS