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Updated: Jan 20, 2026

Intracortical Inhibition Within the Primary Motor Cortex Can Be Modulated by Changing the Focus of Attention
Published on: September 11, 2017
Lack of evidence for interhemispheric inhibition in the lower face primary motor cortex
Francesca Ginatempo1, Nicoletta Manzo2, John C Rothwell3
1Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100 Sassari, Italy.
Objective:
To investigate interhemispheric inhibition (IHI) between the facial primary motor cortices (fM1s).
Methods:
IHI was investigated in 10 healthy subjects using paired-pulse TMS in the depressor anguli oris (DAO), upper trapezius (UT) and first dorsal interosseous (FDI) muscles. Conditioning stimuli (CS) of 90-130% resting motor threshold (RMT) preceded test motor evoked potentials (MEPs) by 7 interstimulus intervals (ISIs) ranging 4-12 ms. In the DAO, we also examined IHI at 1-2 ms ISIs.
Results:
IHI was detected in the UT (CS 130% RMT; ISI 8 ms; p = 0.02) and FDI (CS 120% and 130% RMT, at 8-10 ms ISIs; p = 0.004), but not in DAO at any ISI, instead, there was facilitation at 1-4 ms ISIs and 110-130% RMT CS. In the DAO, conditioned responses at 1-4 ms ISIs were significantly larger than both test MEPs and the response induced by the CS alone.
Conclusion:
In the DAO there was no evidence of IHI even though this was clear in hand and axial muscles. Control experiments excluded a transcallosal origin of the facilitation observed at the shortest intervals.
Significance:
Data suggest that integrated bilateral control of facial muscles occurs mainly at the level of brainstem circuits engaged by corticobulbar output from fM1.
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