Inhibition of Ipsilesional M1 β Oscillations by Contralesional M1 Following Acute Ischemic Stroke: A TMS-EEG Study

BACKGROUND: This study aimed to investigate neurophysiological mechanisms underlying functional impairment and recovery after acute ischemic stroke using transcranial magnetic stimulation combined with electroencephalography, focusing on interhemispheric interactions and oscillatory dynamics. METHODS: This single-center case-control study (December 2022 to May 2024) included 19 ischemic stroke patients within 14 days of symptom onset (mean age, 47.95±12.41 years; 15 [79%] men) with 3-month poststroke follow-up. Sixteen age-matched healthy controls (53.56±9.83 years; 12 [80%] men) were included. Transcranial magnetic stimulation-evoked electroencephalography potentials, local mean field power during 25 ms and 35 ms (local mean field power 25 –35 ms ), and power spectral density of the ipsilesional primary motor cortex (ilM1) were calculated when single-pulse transcranial magnetic stimulation was sequentially applied to the contralesional M1 (clM1) and ilM1. Spearman correlation analysis evaluated associations between transcranial magnetic stimulation combined with electroencephalography parameters and clinical outcomes: Fugl-Meyer assessment, Fugl-Meyer assessment-upper extremity subscale, National Institutes of Health Stroke Scale, and National Institutes of Health Stroke Scale changes from baseline to 3 months poststroke. RESULTS: Stroke patients exhibited simplified transcranial magnetic stimulation-evoked electroencephalography potential waveforms with reduced amplitudes compared with healthy controls. The contralesional resting motor threshold of stroke patients was significantly lower compared with healthy controls ( t =−2.79; P =0.009). The contralesional resting motor threshold was positively associated with the local mean field power 25 –35 ms of ilM1 with stimulation on ilM1 ( r =0.482; P =0.018). The power and power spectral density of β oscillations were negatively associated with the Fugl-Meyer assessment ( r =−0.557, P =0.014; r =−0.417, P =0.038, respectively) and Fugl-Meyer assessment-upper extremity ( r =−0.503, P =0.014; r =−0.389, P =0.05, respectively), but the power of β oscillations was positively associated with changes in the National Institutes of Health Stroke Scale ( r =0.507; P =0.027) with stimulation on clM1. CONCLUSIONS: Increased excitability of the clM1 is associated with decreased excitability of the ilM1. The inhibition of β oscillations in the ilM1 by the clM1 serves as a biomarker for poststroke functional impairment and recovery. Neuromodulation of the clM1 to enhance the β oscillations of ilM1 may be a promising treatment strategy.