Techniques and mechanisms of action of transcranial stimulation of the human motor cortex.

Electrical and magnetic methods are available to stimulate the human brain through the intact scalp. Although both are successful, magnetic stimulation is now used almost exclusively because the discomfort is minimal compared with that caused by electrical stimulation. Nevertheless, electrical stimulation is still used occasionally since comparison of results from both techniques can often yield useful clinical and scientific information not available from either method in isolation.