Simultaneously stimulating both brain hemispheres by rTMS in patients with unilateral brain lesions decreases interhemispheric asymmetry

Abstract

Background: Interhemispheric asymmetry is common in brains with lesions and can be an adverse factor in the recovery of patients from neurological deficits. This study aimed to investigate the influence of repetitive transcranial magnetic stimulation (rTMS) on EEG power in patients with unilateral brain lesions by simultaneously stimulating both brain hemispheres and to elucidate asymmetrical changes in neurophysiological activity induced by rTMS. Methods: Fourteen patients with unilateral brain lesions were treated with one session of 10 Hz rTMS over the vertex. Resting-state EEGs were recorded before and immediately after rTMS. The brain symmetry index (BSI), calculated from a fast Fourier transform, was used to quantify the power asymmetry in both hemispheres and paired channels over the whole frequency range and five frequency bands (delta, theta, alpha, beta and gamma bands). Results: The results indicated that rTMS significantly reduced the BSI in patients with unilateral brain lesions over the entire frequency range (t=2.767, P=0.016). Among the five frequency bands, rTMS only induced a noticeable decrease in the BSI in the delta band (t=2.254, P=0.042). An analysis of different brain regions showed that significant changes in the BSI of the alpha band were found only in the posterior parietal lobe. EEG topographic mapping was employed to identify changes in cortical oscillations across brain regions, and demonstrated a decreased power of delta oscillations in the ipsilesional hemisphere and distinct cortical oscillations in the alpha band around the parietal-occipital lobe in the contralesional hemisphere. Conclusions: When both brain hemispheres are activated simultaneously, rTMS decreases interhemispheric asymmetry primarily through reducing the delta wave in the lesioned hemisphere.