Effects of alcohol on TMS-evoked N100 responses

TMS combined with simultaneous EEG is a novel brain imaging tool allowing investigation local excitability of human cortex. As alcohol acts through increasing function of A-type gamma-aminobutyric acid receptors and attenuating the function of glutaminergic NMDA-receptors-related excitation, we tested whether TMS-evoked N100 response which is thought to reflect cortical inhibitory processes, might be affected by alcohol. Ten healthy subjects ingested alcohol (0.8 g/kg) and EEG responses from 60 channels before and after alcohol ingestion were recorded after left motor-cortex stimulation. Alcohol almost abolished TMS-evoked N100 response. Control experiments with a piece of plastic placed between the head and coil to exclude auditory artefacts were conducted. Alcohol effects were similar when EEG responses from control experiments were subtracted from real-TMS. Alcohol-induced decrease was similar at ipsilateral, contralateral and frontal EEG sites suggesting that alcohol may change cortico-cortical connectivity of motor cortex. Alternative explanation is that alcohol has overall suppression effect on motor cortex. N100 may provide a useful marker of neural inhibition of human cortex for drug research.