Transcranial Magnetic Stimulation (TMS) Simply Explained

1. What It Is About

Transcranial magnetic stimulation, or TMS for short, is a non-surgical treatment. A coil is held against the head and sends short magnetic pulses through the skull. These pulses reach the brain and temporarily change the activity of nerve cells in a small area. 'Transcranial' means 'through the skull'. No anaesthesia or procedure is required.

When the pulses are given in rapid succession, this is called repetitive TMS, abbreviated rTMS. The idea behind it is that the many pulses should readjust brain networks for longer than a single session. Modern TMS was developed by Barker in 1985. A particularly brief form is called theta-burst stimulation; it lasts only a few minutes.

TMS is used in two ways. As a treatment it targets specific brain regions, usually over the forehead area. As a measurement tool, single or paired pulses test how excitable the cerebral cortex is. Regulatory authorities have approved rTMS for depression that has not responded to other treatments, as well as for depression with anxiety disorder, for obsessive-compulsive disorder and for substance-use disorders such as smoking cessation 10.

2. What Studies Show

The effect is best established in depression. A review summarised 34 randomised studies with 2705 children, adolescents and young adults 5. Randomised means the participants were allocated to the treatment groups by chance. In the analysis, depressive symptoms decreased, most markedly with high-frequency stimulation over the left forehead area; that is, the pulses came in very rapid succession. A very brief stimulation form, theta-burst stimulation, showed no reliable advantage in this analysis.

TMS has also been tested after stroke. A review of 74 randomised studies with 5478 patients examined cognitive and memory performance 1. The brief theta-burst stimulation ranked highest: in tests of attention and memory and in questions about everyday life.

For sleep disorders, a review summarises randomised studies 7. People with insomnia, that is persistent problems falling and staying asleep, reported better sleep quality under rTMS than under a sham treatment. Sham treatment, in English 'sham', means the device runs but hardly any stimulation reaches the participant. This allows testing whether an effect really comes from the pulses.

For adolescents with depression and self-harm there is a randomised study with 160 in-patient patients aged 12 to 18 years 6. All received rTMS over the left forehead area; half also received group therapy. After four weeks mood had improved in both groups, more markedly in the group that also received group therapy. This single study is an indication, not proof.

3. What Remains Unclear

Notably, a study protocol on TMS concerns obsessive-compulsive disorder, not depression. For obsessive-compulsive disorder a large study with 250 adults is under way 2. It tests whether low-frequency stimulation over a specific brain area adds benefit to exposure therapy. Results are still awaited.

It is also open whether results from treatment-resistant courses can be transferred to other courses. In people with schizophrenia who hear voices, it was examined whether the electric field strength generated in the tissue can predict improvement 3. Whether this holds is a testable question. For accelerated theta-burst protocols, that is multiple sessions within a short period, reviews note the need for data on the durability of the effect 9. It remains a hypothesis that such protocols could shorten the conventional six-week duration. For inflammation, gut, bone and immune system the question has been raised but not yet decided.

4. What This Means in Everyday Life

TMS is not a single treatment but a family of procedures. They differ in where on the head stimulation is applied, how rapidly the pulses come and how long a session lasts. Therefore it is not possible to make a blanket statement about what 'TMS' achieves. The most robust findings are in depression and in cognitive and memory problems after stroke.

Safety and tolerability form their own large block of controlled studies. This speaks for systematic testing, but does not mean the procedure is free of side effects.

Single and paired pulses measure the excitability of the cerebral cortex. This is a marker of system function, not a diagnosis of a disorder.

Much has been studied in treatment-resistant courses, that is in people for whom other treatments have not worked. Whether the results also apply to other courses is the next question that studies must clarify.

All details with study numbers and sources: detailed page on Transcranial Magnetic Stimulation (TMS). For children: Transcranial Magnetic Stimulation (TMS) for children.