Changes in Neuronal Activity after Low Frequency Repetitive Transcranial Magnetic Stimulation

Kim, Hee Jin; Lee, Mina; Cho, Hyun Jee; Park, Kee Duk; Choi, Kyoung Gyu; Lee, Hyang Woon

Abstract

BACKGROUND
S: A one Hz repetitive transcranial magnetic stimulation (rTMS) on the motor cortex is known to decrease motor cortical excitability locally, but the effects on distant areas or at different time points remain unclear. We investigated the spatiotemporal changes in cortical neuronal activity induced by local suprathreshold 1 Hz rTMS. METHODS: Fourteen healthy subjects underwent daily rTMS for 5 consecutive days (1 Hz, 110% of resting motor threshold, 1800 stimuli) over the right temporal cortex (T4 of 10-20 international EEG system). EEG signals were collected at 19 electrodes baseline, before and after each rTMS session, and 2 weeks after the last rTMS session. Band powers of 2-4, 4-8, 8-13, 13-20, 20-40 Hz were calculated. Cross correlation (CC), mutual information (MI), and correlation dimension (D2), the maximum Lyapunov exponent (Lmax) were tested to investigate changes of EEG dynamics of synchronization and complexity. Wilcoxin signed ranks test was used for statistical analysis. RESULTS: One Hz rTMS immediately caused a significant increase in alpha, gamma, theta band powers and the Lmax (p<0.0001 to 0.041, p<0.0001 to 0.038, respectively) in ipsilateral and contralateral hemispheres after daily rTMS. CC and MI decreased after daily rTMS sessions at the right frontocentrotemporal and left frontotemporal areas (p<0.001 to 0.041). CONCLUSIONS: These findings suggest that focal 1 Hz rTMS can induce a short-term increase in the neuronal complexity and de-synchronization of local neuronal networks at stimulated and distant cortical areas. These findings raise a possibility of therapeutic applications of low frequency rTMS in patients with an abnormally excitable brain cortex such as epilepsy or movement disorders.