Improving brain function with transcranial magnetic stimulation?

Stimulation of the cerebral cortex has played an integral role in the development of clinical neuroscience, from Penfield’s delineation of the motor homunculus, to the therapeutic techniques of electroconvulsive therapy, to the current use of stimulation to determine the function of epileptic cortex or to identify the language-dominant hemisphere. In 1985, Barker et al.1 introduced transcranial magnetic stimulation (TMS), a technique for electrical stimulation of the cerebral cortex by inducing a strong, rapidly changing magnetic field adjacent to the scalp. Because the calvarium has no impedance to a magnetic field, TMS induces intracortical electrical currents with little or no discomfort. TMS can theoretically be applied to any superficial cortical area. Because the effects of motor cortex stimulation are readily quantified with electromyography (EMG), TMS has been used predominantly in the study of the motor system. For example, Liepert et al.2 used TMS to map the motor cortex to show that exercise of the paretic arm after a stroke, along with restraint of the nonparalyzed arm, increased the size of the motor area for the affected hand. TMS can …