Excitatory magnetic stimulation increased interhemispheric inhibition: a pharmacological and TMS-EEG study

The inhibitory effect of interhemispheric signal propagation (ISP) is believed to be aligned with GABAB receptor mediated inhibitory neurotransmission and related to interhemispheric connectivity. Repetitive Transcranial magnetic stimulation (rTMS) is a safe and potent strategy for altering brain connectivity. However, it remains unclear if rTMS modulates ISP. With pretreatment of baclofen, a GABAB receptor agonist, this study characterized rTMS effects on ISP and the influence of GABAB receptor neurotransmission. ISP was measured with TMS and electroencephalography co-registration (TMS-EEG). Excitatory rTMS (> 5 Hz) was found to increase interhemispheric inhibition indexed by ISP. This effect was reduced by baclofen pretreatment, potentially reflecting competition for GABAB receptors neurotransmission between baclofen and rTMS. Beyond evoked potentials, our data also identified TMS-evoked gamma oscillation as a reliable indicator of intracortical inhibition. These novel findings help to clarify the effects of rTMS on interhemispheric connectivity, which may help to optimize rTMS treatments for various psychiatric disorders.