Transcranial magnetic stimulation (TMS) is a non-invasive medical procedure that uses magnetic fields to influence brain activity. Operating without surgery, this therapeutic tool introduces changes to nerve cells from outside the body. As a developing approach, its applications and understanding continue to expand within the medical community.
The Science Behind TMS
The core of transcranial magnetic stimulation lies in its use of electromagnetic induction. A specialized device with a magnetic coil is positioned against a person’s scalp. This coil generates focused magnetic pulses designed to pass through the skull and overlying tissues without causing harm. These magnetic fields are rapidly turned on and off, creating a changing magnetic environment.
This changing magnetic field induces a small and precise electrical current within a targeted region of the brain. This induced current is localized to the area directly beneath the coil, often a part of the prefrontal cortex. The electrical current is strong enough to depolarize or hyperpolarize neurons, which means it can either excite the nerve cells into firing or make them less likely to fire.
The frequency of the magnetic pulses determines their effect. High-frequency pulses are used to increase brain activity, while low-frequency pulses tend to reduce it. Over a course of treatments, these induced changes can lead to lasting alterations in brain function, a process known as neuroplasticity.
Conditions Treated with TMS
The U.S. Food and Drug Administration (FDA) has approved transcranial magnetic stimulation for several conditions, primarily when initial treatments have proven insufficient. Its most established application is for Major Depressive Disorder (MDD) for individuals who have not experienced adequate improvement from antidepressant medications. For these patients, TMS offers a non-pharmacological alternative.
Beyond depression, the FDA has expanded its approved uses. In 2018, TMS was cleared for the treatment of Obsessive-Compulsive Disorder (OCD). Another approved application is for anxious depression, a condition where symptoms of anxiety and depression co-occur. The scope also includes aiding in smoking cessation and treating the pain associated with migraine headaches, while research into other uses is ongoing.
The Patient Experience
A person undergoing TMS therapy is awake and seated comfortably in a reclining chair. The first session is typically the longest because it involves a “mapping” process. During this initial step, the clinician determines the precise location for coil placement and the appropriate magnetic field strength. This is done by stimulating the motor cortex and observing for a slight twitch in the hand to establish a baseline motor threshold.
Once mapping is complete, the treatment sessions can begin. A session involves the electromagnetic coil being placed against the scalp at the predetermined location. When the device is active, patients hear clicking sounds and feel a tapping sensation on their scalp beneath the coil. This sensation is well-tolerated, and the intensity is calibrated for comfort and effectiveness.
A single treatment session lasts between 20 and 40 minutes. A complete course of therapy requires multiple sessions, often occurring daily for four to six weeks. A notable aspect is the absence of downtime; individuals can drive home and resume normal activities immediately after each appointment.
Potential Side Effects and Safety Considerations
The safety profile of TMS is well-documented, with most side effects being mild and temporary. The most frequently reported issues are headaches and discomfort at the stimulation site on the scalp. Some individuals may also experience lightheadedness or twitching of facial muscles during the delivery of the pulses, though these effects typically diminish over the course of treatment.
Serious risks are uncommon. The most significant potential risk is the induction of a seizure, but this is a rare event with an estimated risk of less than one in 10,000 sessions. To ensure patient safety, technicians follow established protocols and screen patients thoroughly before beginning treatment.
Unlike other brain stimulation therapies, TMS does not require anesthesia or sedation, which eliminates the risks associated with those medications. It also does not cause the systemic side effects often seen with antidepressant medications, such as weight gain or memory impairment, as the stimulation is localized.
Candidate Eligibility
Determining who is a suitable candidate for TMS involves a careful screening process. The primary concern is the presence of any non-removable metal in or near the head, as the powerful magnetic fields could move or heat these objects. This includes items like aneurysm clips or coils, stents in the neck or brain, cochlear implants, or bullet fragments. Standard dental fillings and braces are not a problem.
An individual’s medical history is also a factor in eligibility. People with a history of seizures, epilepsy, or other neurological conditions that could increase the risk of a seizure are not candidates for TMS. A thorough evaluation by a qualified healthcare provider is necessary to review a patient’s medical and treatment history to ensure the procedure is both appropriate and safe.