Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive medical procedure that influences brain activity using magnetic fields. This technique is a form of neuromodulation, aiming to adjust neural function without direct physical intervention. It involves delivering repetitive pulses of a magnetic field to specific brain regions from a coil placed on the scalp, modulating neural activity in targeted areas.
The Scientific Basis of rTMS
The core principle behind rTMS is rooted in electromagnetic induction, a concept formulated by Michael Faraday in 1831.
During an rTMS session, an electrical current rapidly discharges through a copper wire coil encased in a plastic shell. This coil is positioned near the patient’s scalp. The rapidly changing electrical current within the coil generates a powerful, focused magnetic field that passes unimpeded through the skull and into the brain tissue beneath.
According to the principle of electromagnetic induction, this magnetic field then creates a small, precise electrical current within the targeted brain region. This induced electrical current is strong enough to stimulate neurons, causing them to depolarize and generate action potentials.
Repeated stimulation can lead to lasting changes in brain connectivity and activity. This phenomenon is referred to as neuroplasticity, the brain’s ability to reorganize itself by forming new or strengthening existing neural connections. High-frequency rTMS (above 1 Hz) increases cortical excitability, while low-frequency rTMS (1 Hz or less) decreases it. These modulatory effects on cortical excitability are the mechanism behind rTMS’s therapeutic benefits.
Medical Applications of rTMS
Repetitive transcranial magnetic stimulation has received U.S. Food and Drug Administration (FDA) approval for several conditions, for cases where other therapies have not been successful. Major Depressive Disorder (MDD) was the first condition approved in 2008, specifically for patients unresponsive to antidepressant medication. This treatment targets brain regions involved in mood control, such as the left dorsolateral prefrontal cortex, aiming to activate areas that show decreased activity in depression.
Obsessive-Compulsive Disorder (OCD) also gained FDA approval, with specific protocols cleared in 2018 and 2020. For OCD, rTMS targets components of the cortical-striatal-thalamocortical circuit, including the medial prefrontal cortex and anterior cingulate cortex. It is also approved to help adults quit smoking and for anxious depression.
Beyond these approved uses, rTMS is being researched for several “off-label” applications. This includes anxiety disorders, such as generalized anxiety disorder, social anxiety disorder, and post-traumatic stress disorder (PTSD). Studies are exploring its use for chronic pain conditions, including fibromyalgia and neuropathic pain, as well as for stroke recovery and various neurological disorders like Parkinson’s disease.
The Patient Treatment Process
The rTMS treatment process begins with an initial assessment to determine the appropriate treatment location and energy level. A treating psychiatrist performs threshold testing to tailor the magnetic pulse strength for the individual patient. This mapping ensures the machine’s intensity is set to effectively stimulate the intended brain region.
During an rTMS session, the patient is seated comfortably in a reclining chair and remains awake and alert throughout the procedure. An electromagnetic coil is precisely positioned against the patient’s scalp, near the front region of the brain, and then activated. Patients describe the sensation as a tapping or clicking feeling on the scalp, which subsides as treatment progresses. The machine also produces a rapid, woodpecker-like tapping sound, so earplugs are provided to reduce the noise.
A single rTMS session lasts between 20 to 45 minutes, depending on the specific treatment protocol. A standard course of treatment involves daily sessions, five days a week (Monday through Friday), for a period of four to six weeks. Patients can resume their normal daily activities immediately after each session, as no anesthesia or sedation is required.
Side Effects and Contraindications
Repetitive transcranial magnetic stimulation is considered a safe and well-tolerated procedure, with most side effects being mild and temporary. The most common side effects include headaches or discomfort at the treatment site on the scalp, muscle contractions or tingling in the scalp, jaw, or face during the procedure, or brief lightheadedness. These effects improve shortly after a session and can be managed with over-the-counter pain relievers.
A rare but serious risk associated with rTMS is seizure induction. The risk of seizure is very low, estimated at fewer than 3 patients per 100,000 sessions. While seizures are uncommon, the risk can be influenced by factors such as pre-existing neurological conditions, changes in medication, or substance use, particularly excessive alcohol consumption or withdrawal.
Specific contraindications prevent individuals from receiving rTMS. The presence of any non-removable magnetic-sensitive metal implants or devices in the head or body is an absolute contraindication. This includes items such as aneurysm clips, stents, cochlear implants, or implanted medication pumps, as the magnetic fields could interfere with or malfunction these devices. A history of a seizure disorder also precludes a patient from receiving rTMS treatment.