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From the Departments of Neurology and Neuropsychology, McKnight Brain Institute at the University of Florida, Gainesville, Florida
Address correspondence and reprint requests to Dr. William J. Triggs, 100 S. Newell Drive, L3-100 McKnight Brain Institute Gainesville, FL 32610-0236; e-mail: triggswj{at}neurology.ufl.edu
Background: There is considerable evidence that emotions are expressed more intensely on the left side of the face. This asymmetry could reflect a right hemisphere advantage in processing emotional material or an asymmetry in corticobulbar motor systems. Transcranial magnetic stimulation (TMS) was used to test for lateralized asymmetry in the cortical control of muscles of facial expression in the lower face
Methods: We administered TMS to the motor cortex of 50 subjects during contraction of bilateral orbicularis oris muscles. We analyzed motor evoked potentials (MEPs) with a repeated measures analysis of variance (ANOVA) using hemisphere stimulated and orbicularis oris side recorded as within subject factors
Results: TMS elicited contralateral MEPs in 42 of 50 subjects. Forty of these 42 subjects showed bilateral MEPs. The ANOVA showed a significant main effect of face side, such that MEPs elicited in left face were larger than in right face (p < 0.0001). The analysis also showed a significant interaction between the hemisphere stimulated and face side, such that the difference between contralateral and ipsilateral MEPs with right brain TMS was greater than with left brain TMS (p < 0.0001)
Conclusions: The results provide evidence of lateralized asymmetry of corticobulbar projections to muscles of facial expression in the lower face.
Disclosure: The authors report no conflicts of interest.
Supported by NIMH MH-623539.
Presented in part at the 54th annual meeting of the American Academy of Neurology, Denver, CO, April 17, 2002.
Received October 20, 2004. Accepted in final form May 17, 2005
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