Activation of neurons not only changes their membrane potential and firing rate but, as a secondary action reduces membrane resistance. This loss of resistance, or increase of conductance, may be of central importance in non-invasive magnetic or electric stimulation of the human brain since electrical fields cause larger changes in transmembrane voltage in resting neurones with low membrane conductances than in active neurones with high conductance. This may explain why both the immediate and after-effects of brain stimulation are smaller or even reversed during voluntary activity compared to rest. Membrane conductance is also increased during shunting inhibition, which accompanies the classic GABAa IPSP. This short-circuits nearby EPSPs and is suggested here to contribute to the magnitude and time course of short latency intracortical inhibition (SICI) and facilitation (ICF). This article is protected by copyright. All rights reserved
