Transcranial magnetic stimulation (TMS) is an established technique in which a painless pulse of fast rising magnetic field is used to induce an electric current intracranially, causing depolarisation of nerve membranes and the generation of action potentials. It produces early motor responses trans-synaptically via the pyramidal tract. There are other effects, which are subject to changes in the GABAergic and monoaminergic systems and in sodium and calcium channel properties,¹ the first of these showing particular relevance to human plasticity.² In addition to the familiar clinical studies of central motor conduction time, TMS is used for single motor unit studies, mapping of the motor cortex, the determination of motor threshold or cortical excitability, intracortical inhibition and facilitation studies (using a paired pulse protocol, to express interneuronal connectivity involving the motor cortex), stimulus-response recruitment curves, sensory studies (including the production of phosphenes), and for the targeted disruption of motor or cognitive task . . . [Full text of this article]