Excitability prediction of the motor cortex leg representation using EEG-TMS

Corticospinal excitability of the motor cortex (M1) hand representation is predicted by phase and power of the sensorimotor mu-rhythm in EEG-TMS studies. Here we address for the first time corticospinal excitability prediction of the M1 leg representation.

In 16 healthy subjects, 1,000 trials of single-pulse navigated focal TMS to the hot spot of the tibialis anterior muscle were obtained during motor evoked potential (MEP) and EEG recording, using Hjorth montages centered over sensorimotor cortex, ipsilateral to the hemisphere that was targeted by TMS.

Power in the high gamma frequency bands correlated directly, and power in the beta band inversely with MEP amplitude. The phase of the mu-rhythm had no effect but a significant interaction between mu-power and mu-phase was observed: with high mu-power, largest MEPs occurred during the early peak, while with low mu-power largest MEPs were observed during the late peak.

Findings demonstrate that an interaction of mu-power and -phase, and power in other frequency bands of the EEG signal from the sensorimotor cortex prior to the TMS pulse predict corticospinal excitability of the M1 leg representation.

Findings may inform brain-state dependent stimulation of M1 leg representation for treatment of gait or balance disorders.