V36. Characterization of GABAA-receptor mediated neurotransmission in the human cortex by paired-pulse TMS-EEG

Abstract

Objective To determine the physiology of short-interval intracortical inhibition (SICI) directly at the cortical level. Methods We recorded a 64 channel EEG during application of a magnetic test stimulus (TS100) 2 ms after a conditioning stimulus (CS70) over the left primary motor cortex at an intensity of 100% and 70% resting motor threshold for the right APB muscle, respectively. Subjects were given a single oral dose of diazepam or baclofen in this placebo controlled, pseudo-randomized, double-blinded crossover study. Results CS70 evoked clearly discernible and reproducible EEG potentials (TEPs) similar to TS100, i.e. a P25, N45, P70, N100, and P180 potential. In the paired-pulse condition, corrected for these CS70-induced TEPs, CS70 modulated all TS-evoked EEG potentials, i.e. suppressed the P25, N45, N100, and P180, whereas the P70 was increased. Preliminary analyses of the pharmacological data from eleven subjects further suggested an increase of SICI of the P25 potential by diazepam, in line with a GABAA-receptor mediated mechanism. Conclusions Our data provide evidence for the physiological mechanisms of SICI at the level of the human cortex with high temporal and spatial resolution. Key message SICI is characterized by temporally and spatially distinct modulation of TMS-evoked EEG responses.