Reduced mirror neuron activity in schizophrenia and its association with theory of mind deficits: evidence from a transcranial magnetic stimulation study.
BACKGROUND
The "mirror-neuron system" has been proposed to be a neurophysiological substrate for social cognition (SC) ability. We used transcranial magnetic stimulation (TMS) paradigms to compare putative mirror neuron activity (MNA) in 3 groups: antipsychotic-naive, medicated schizophrenia patients, and healthy comparison subjects. We also explored the association between MNA and SC ability in patients.


METHODS
Fifty-four consenting right-handed schizophrenia patients (33 antipsychotic naive) and 45 matched healthy comparison subjects completed a TMS experiment to assess putative premotor MNA. We used 4 TMS paradigms of eliciting motor-evoked potentials (MEP) in the right first dorsal interosseous (FDI) muscle. These were applied while the subjects observed a goal-directed action involving the FDI (actual action and its video) and a static image. The difference in the amplitude of the MEP while they observed the static image and the action provided a measure of MNA. Subjects also underwent SC assessments (theory of mind [ToM], emotion processing, and social perception).


RESULTS
Two-way repeated measures ANOVA revealed significant group × occasion interaction effect in 3 TMS paradigms, indicating deficient motor facilitation during action observation relative to rest state in antipsychotic-naive schizophrenia patients as compared with the other two groups. Among patients, there were significant direct correlations between measures of MNA and ToM performance.


CONCLUSIONS
Antipsychotic-naive schizophrenia patients have poorer MNA than medicated patients and healthy controls. Measures of putative MNA had significant and consistent associations with ToM abilities. These findings suggest a possibility of deficient mirror neuron system underlying SC deficits in schizophrenia.
Department of Psychiatry, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, Karnataka, India; urvakhsh@gmail.com.
Urvakhsh Meherwan
UM
Mehta
Department of Psychiatry, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, Karnataka, India;
Jagadisha
J
Thirthalli
Department of Psychiatry, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, Karnataka, India;
Rakshathi
R
Basavaraju
Department of Psychiatry, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, Karnataka, India;
Bangalore N
BN
Gangadhar
Department of Neurology, Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA.
Alvaro
A
Pascual-Leone
D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use; D002540:Cerebral Cortex / Q000503:physiopathology*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D059167:Mirror Neurons / Q000502:physiology*; D012559:Schizophrenia / Q000188:drug therapy / Q000503:physiopathology*; D012938:Social Perception; D056345:Theory of Mind / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
D014150:Antipsychotic Agents
antipsychotic-naive; embodied simulation; mental state attribution; mirror neurons; psychosis; social cognition