Transcranial magnetic stimulation (TMS) is a technique for noninvasive stimulation of the human brain. Stimulation is produced by generating a brief, high-intensity magnetic field by passing a brief electric current through a magnetic coil. The field can excite or inhibit a small area of brain below the coil. All parts of the brain just beneath the skull can be influenced, but most studies have been of the motor cortex where a focal muscle twitch can be produced, called the motor-evoked potential. The technique can be used to map brain function and explore the excitability of different regions. Brief interference has allowed mapping of many sensory, motor, and cognitive functions. TMS has some clinical utility, and, because it can influence brain function if delivered repetitively, it is being developed for various therapeutic purposes.

Transcranial magnetic stimulation (TMS) is rapidly developing as a powerful, non-invasive tool for studying the human brain. A pulsed magnetic field creates current flow in the brain and can temporarily excite or inhibit specific areas. TMS of motor cortex can produce a muscle twitch or block movement; TMS of occipital cortex can produce visual phosphenes or scotomas. TMS can also alter the functioning of the brain beyond the time of stimulation, offering potential for therapy.

Patients with Parkinson's disease were asked to make ballistic elbow flexion movements of 10, 20 and 40 degrees. Normal subjects made all these movements in the same amount of time with a single 'triphasic' EMG pattern of successive bursts in biceps, triceps and biceps. Almost all the patients made some movements requiring additional cycles of alternating biceps and triceps activity. Most of the patients exhibited at least one example of a longer movement taking more cycles than a shorter movement. It is argued that this behaviour explains previous kinematic analyses of movement in patients with Parkinson's disease and represents a physiological mechanism of bradykinesia. In part on the basis of the data presented here, it is suggested that a normal role of the basal ganglia in movement is to energize the appropriate muscles required to make the movement.