Information Brochure on
Repetitive Transcranial Magnetic Stimulation (rTMS)

rTMS Committee of IFCN
International Federation of Clinical Neurophysiology

Transcranial magnetic stimulation or TMS is a neurophysiologic technique that allows the induction of a current in the brain using a magnetic field to pass the scalp and the skull safely and painlessly. In TMS, a current passes through a coil of copper wire that is encased in plastic and held over the subject’s head. This coil resembles a paddle or a large spoon and is held in place either by the investigator or by a mechanical fixation device similar to a microphone pole. As the current passes through the coil it generates a magnetic field that can penetrate the subject’s scalp and skull and in turn induce a current in the subject’s brain. There is a clicking noise associated with the current passing in the coil, but the effect of the magnetic field and the induction of current in the brain are not painful. However, some discomfort may occur from the contraction of scalp muscles or the activation of nearby nerves. 

TMS was introduced in the mid 1980’s and is used in clinical neurophysiology to study the nerve fibers that carry the information about movements from the brain cortex to the spinal cord and the muscles. This technique is felt to be safe and is part of standard clinical tests in neurology in many countries worldwide. 

Technical developments in the devices used for TMS made it possible in the late 1980’s to apply TMS in trains of multiple stimuli per second. This form of TMS is called repetitive TMS or rTMS. In rTMS, stimuli are applied to the same brain area several times per second during several consecutive seconds. The number of stimuli per second, the strength of the stimuli, the duration of the train of stimulation, the interval between trains, the total number of trains and the total number of stimuli in a given session or to a given brain position can all be varied. All these aspects of rTMS are referred to as stimulation parameters. Repetitive TMS is an exciting tool in research on brain function, but it remains experimental at this point. There are potential adverse effects of rTMS and great caution is required when utilizing rTMS in studies. 

Repetitive TMS can be used to study how the brain organizes different functions such as language, memory, vision, or attention. In addition, rTMS seems capable of changing the activity in a brain area even beyond the duration of the rTMS application itself. In other words, it seems possible to make a given brain area work more or less for a period of minutes, hours, days or even weeks when rTMS is applied repeatedly several days in a row. This has opened up the possibility of using rTMS for therapy of some illnesses in neurology and psychiatry. However, this therapeutic potential of rTMS is still being studied and should not be considered proven.

Generally, in rTMS studies, subjects perform some motor, visual, or behavioral tasks, for example a computer test before and after or during receiving rTMS. Repetitive TMS can be applied in a single session or in different sessions on different days. A single or multiple brain areas might be targeted by rTMS depending on the reason for the study. Generally the investigators are interested in studying if and how rTMS changes a given brain function or the symptoms of a given disease.

Since rTMS is experimental, subjects should undergo rTMS only in the context of a research protocol that is approved by an Institutional Ethics Committee. Before entering the research protocol subjects should understand the purpose of the study, the design of the study, the form and amount of rTMS that they will receive. In addition, subjects should be informed about the potential risks and adverse effects of rTMS and the steps taken to prevent them. All subjects should be asked to sign an informed consent form before the study begins.

The main concern when using rTMS is its potential to induce a seizure or epileptic convulsion, even in subjects without any predisposing illness. This risk is low, in the order of 1 in 1000 studies or less. In addition, investigators using rTMS have developed safety guidelines that advice on the appropriate parameters of stimulation to use in order to minimize the risk of a seizure. It is important to note that experiencing a seizure induced by rTMS has never led to the development of epilepsy or posed any risk for subsequent unprovoked seizures. In addition, rTMS induced seizures would occur during the rTMS study or immediately after. Seizures induced by rTMS cannot be expected to affect the subject hours or days after the rTMS. Overall, less than 10 seizures caused by rTMS have been reported in the world’s literature and most of them occurred in the setting of early studies designed to evaluate the safety of rTMS. Nevertheless, a seizure is a possible adverse effect of rTMS and the laboratories in which rTMS is conducted are fully equipped for the emergency treatment of such an adverse effects. The person performing rTMS will be properly trained in diagnosing and treating a seizure. In addition, subjects undergoing rTMS will be closely monitored. Particularly in studies applying rTMS close to recommended safety guidelines, monitoring may include video and neurophysiologic recording of the activity in the brain (EEG) and the muscles (EMG). Monitoring will help detect the earliest sign of a seizure and prevent its occurrence.

Other potential adverse effects of rTMS include the induction of a muscle tension headache or a neck ache in approximately 3 of every 100 subjects studied. These are generally mild discomforts that respond promptly to an aspirin, acetaminophen (Tylenol ®) or other common analgesics.

Repetitive TMS can also cause ringing in the ears or even transient hearing loss if the subjects do not wear earplugs during the rTMS studies. Earplugs prevent this risk.

Repetitive TMS can also cause memory problems and other cognitive deficits. These adverse effects appear to be very rare, mild, and very transient. Most studies on rTMS have not found any adverse effects of rTMS on mental abilities. Nevertheless, few studies have reported such adverse effects and they should be taken seriously and appropriate testing for such potential side effects might be conducted.

Finally, it is important to realize that rTMS has only been studied for little over ten years and there probably is still much that needs to be learned about it. Even though animal studies have not shown any risks of brain damage or longterm injury to the brain or its functions after rTMS, the data in humans are still very few. Therefore, adverse effects that cannot be foreseen today are theoretically possible.

Subjects considering their participation in a rTMS study should know that there are relative and absolute contraindications to rTMS. Subjects with metal anywhere in the head, excluding the mouth, is generally a contraindication to rTMS. This includes shrapnel, and screws and clips from surgical procedures unless the physical properties of the metal object are known and there is a strong reason for using rTMS. Subjects with cardiac pacemakers and implanted medication pumps should not participate in most rTMS studies. TMS also should not be performed in patients with electrodes inside the heart which might provide a low-resistance current path to electrically sensitive tissue. Persons with serious heart disease are at increased risk in the event of a seizure, and unless the potential clinical benefit outweighs the risk, they should not participate in rTMS studies. Persons with increased intracranial pressure, as in acute large infarctions or trauma, are also at increased risk in the event of a seizure, and should not receive rTMS. Pregnant women or women in child bearing age that might be pregnant should also be excluded from rTMS studies. Finally, great caution is needed when applying rTMS to subjects with a history of seizures, a family history of epilepsy, and patients taking medication that might increase the risk of seizures.

This information is offered in good faith with the intention that it is accurate and complete. New research may alter the situation at any time. Subjects should discuss proposed studies with researchers and their physicians. Before agreeing to participate in a rTMS study, all the questions of potential subjects should be answered.

If you want to learn more about rTMS you may want to check out these web-sites: 

www.elsevier.com/locate/ifcn

www.ists.unibe.ch

www.musc.edu/tmsmirror/TMSresrc.html

Members rTMS Committee:

Mark Hallett, M.D.
Chairman

R. H. Belmaker, M.D.

Charles M. Epstein, M.D.

Alvaro Pascual-Leone, M.D., Ph.D.

Walter Paulus, M.D.

Paolo Rossini, M.D.

John Rothwell, Ph.D.

Harold Sackeim, Ph.D.

Carlo A. Tassinari, M.D.

Eric Wassermann, M.D.

Officers of IFCN

Carl H. Luecking, M.D.

Hiroshi Shibasaki, M.D.

Paul A. Despland, M.D.

David Burke, M.D.

Paolo Rossini, M.D.

Guenther Deuschl, M.D.