Azienda Ospedaliera Universitaria of Siena 1 article published in JoVE Neuroscience Effects of Transcranial Alternating Current Stimulation on the Primary Motor Cortex by Online Combined Approach with Transcranial Magnetic Stimulation Anna Shpektor1,3, Maria Nazarova4, Matteo Feurra1,2 1School of Psychology, Centre for Cognition and Decision Making, National Research University Higher School of Economics, 2Department of Medicine, Surgery and Neuroscience, Unit of Neurology and Clinical Neurophysiology, Brain Investigation & Neuromodulation Lab. (Si-BIN Lab), Azienda Ospedaliera Universitaria of Siena, 3Department of Experimental Psychology, University of Oxford, 4Centre for Cognition and Decision Making, National Research University Higher School of Economics Transcranial Alternating Current Stimulation (tACS) allows the modulation of cortical excitability in a frequency-specific fashion. Here we show a unique approach which combines online tACS with single pulse Transcranial Magnetic Stimulation (TMS) in order to "probe" cortical excitability by means of Motor Evoked Potentials.