Glossary
Transcranial Magnetic Stimulation
What is transcranial magnetic stimulation?
Transcranial magnetic stimulation (TMS) uses a rapidly changing magnetic field to induce electrical currents in brain tissue. A coil held near the scalp produces the field. Researchers and clinicians use the resulting stimulation for different purposes.
How it works
The principle is electromagnetic induction: a changing magnetic field produces an electric field. Coil shape, position, and orientation affect stimulation. Figure-eight coils generally produce a more concentrated electric field near the meeting point of their two loops; circular coils produce a broader pattern. In a simulation comparing 50 designs, Deng and colleagues found that figure-eight field coils could achieve greater focality, but every design faced a depth–focality tradeoff: reaching deeper required spreading the field more widely. A more focal coil therefore does not isolate one brain region perfectly, and these modeled fields are not a direct measure of each person’s neural response.
Repetitive transcranial magnetic stimulation (rTMS) delivers repeated pulses. In some motor-cortex protocols, higher-frequency stimulation facilitates and lower-frequency stimulation suppresses measured excitability. These are tendencies under particular conditions, rather than universal rules for every region and person.
Research applications
TMS lets researchers examine how changing neural activity relates to perception, cognition, or behavior. The interpretation depends on the stimulation, comparison condition, and outcome measured.
Clinical treatment
Specific devices and protocols have clinical uses, including treatment-resistant depression. NIMH describes rTMS as an FDA-cleared treatment for selected indications. Evidence and authorization apply to the particular treatment, rather than every possible use of TMS.
Neurorehabilitation
TMS has also been investigated in rehabilitation, including after stroke. A proposed effect on neural activity or plasticity is not enough to establish an improvement in daily functioning. The relevant clinical outcome needs to be measured.
Why it matters
TMS connects a physical method of stimulation with questions about brain function and treatment. Keep evidence for the method, the protocol, and the patient group together when assessing a claim.