Motor cortex excitability states in chronic stroke patients probed by EEG-TMS.

OBJECTIVE

In healthy subjects, the trough vs. no-trough phases of the sensorimotor µ-rhythm correspond to high- vs. low-excitability states of the motor cortex (M1). We tested this excitability differentiation in the ipsilesional (iM1) and contralesional M1 (cM1) of chronic stroke patients.

METHODS

19 chronic stroke patients received single-pulse transcranial magnetic stimulation (TMS), separately over the iM1 and cM1, during EEG recordings. High and low M1 excitability states were defined by binning a post-hoc estimate of the µ-phase at TMS delivery. TMS-evoked EEG potentials (TEPs) and time-frequency responses were characterized for excitability states and hemispheres. The motor function of the affected arm was tested by the Fugl-Meyer Assessment Upper Extremity (FMA-UE.

RESULTS

In cM1, TMS at the high- vs. low-excitability state resulted in larger TEP amplitudes and increased post-pulse power in the beta band. In iM1, these modulations were not significant except for post-pulse beta power. This retained excitability differentiation significantly correlated with FMA-UE.

CONCLUSIONS

The degree of excitability differentiation in iM1 depending on phase of the sensorimotor µ-rhythm correlates with individual affected upper extremity motor function.

SIGNIFICANCE

The degree of excitability differentiation in iM1 might serve as a new independent marker of motor recovery.