[ckemere]

TMS relies on Faraday's Law - a large transient magnetic field induces electrical currents in the brain. When these currents are large enough, they perturb the activity of neurons nearby. (Neurons communicate based on pulses of dynamics in the electrical potential across their cell membranes.) There are also second order effects related to the alignment of the neural structure to the induced field lines, etc.

TMS of motor cortex can induce finger twitches and TMS of visual cortex can induce phosphenes or other visual disturbances. Single TMS pulses have effects that wear off very rapidly, but repetitive TMS may be able to induce therapeutic plasticity (it has been reported to potentially induce seizures - following the normal law that nothing medically useful has no side effects).