Transcranial Magnetic Stimulation
Transcranial Magnetic Stimulation
Definition
Transcranial magnetic stimulation (TMS) is a non-invasive experimental procedure that gently stimulates the brain using short bursts of electromagnetic energy.
Description
TMS uses specialized electromagnets that are placed on the patient’s scalp. The magnets generate short bursts of magnetic energy of approximately the same strength as a magnetic resonance imaging (MRI) scanner, but over a more focused area. These pulses produce electrical currents in the brain that change the brain’s activity in the area of focus. Repetitive transcranial magnetic stimulation (rTMS) is treatment using a series of TMS pulses.
Purpose
Originally, TMS was a research tool used to map the brain and to study the differences between a normal brain and a brain with pathology. TMS has been used to study how various functions such as perception, memory, or attention are organized in the brain.
More recently, TMS research has also begun to focus on practical applications for the technology in the treatment of various disorders. Although such treatments are not yet proven to be effective and have not been approved by the Food and Drug Administration for use in the United States, U.S. researchers are currently performing clinical trials . Research is currently underway to investigate the effectiveness of TMS in the treatment of a number of illnesses, most notably major depression .
Use of TMS in the treatment of depression
Much of the application research in TMS has focused on its effectiveness in the treatment of severe and treatment-resistant depression. Although antidepressants, psychotherapy , and electroconvulsive therapy (ECT) are usually effective in the treatment of depression, not all cases can be successfully treated using these methods. In clinical trials, TMS has been found to be effective in many, but not all, of the more difficult cases.
Since the use of antidepressants in children and adolescents is not recommended due to safety issues, TMS offers a promising alternative treatment. However, most research studies to date have focused only on depression in adults. The effectiveness of TMS for children and adolescents cannot be assumed to be the same.
Use of TMS in the treatment of other illnesses
Although most research in the clinical application of TMS and rTMS is focused on the treatment of depression, experimental research and clinical case studies also point to the possibility of TMS being an effective treatment in a number of other disorders. Among these are:
- chronic pain
- epilepsy
- migraine
- obsessive-compulsive disorder
- panic disorder
- Parkinson’s disease
- post-traumatic stress disorder
- rehabilitation following a stroke
- tinnitus
- Tourette’s syndrome
- various psychiatric symptoms, particularly auditory hallucinations associated with schizophrenia
Risks
At this time, it is generally thought that there are no harmful side effects to TMS or rTMS. The main risk of treatment with TMS is of inducing a seizure. Even in cases where seizures resulted from TMS, the seizures occurred either during the treatment or immediately thereafter, and did not lead to the development of epilepsy. In general, the research shows this risk to be low, and safety guidelines have been put in place to minimize seizure risk.
Although there is the potential risk of TMS to affect the normal functioning of the brain, the literature to date reports few side effects such as those resulting from electroconvulsive therapy. As opposed to the potential memory loss, inability to concentrate, or similar side effects often associated with ECT, the side effects of TMS tend to be very rare, mild, and transient.
Potential side effects of TMS include neckaches or headaches. These tend to be generally mild reactions that respond well to common over-the-counter analgesics. rTMS has been shown to cause tinnitus (ringing in the ears) or temporary hearing loss. However, the use of earplugs during the treatment prevents this risk. The long-term risks of rTMS treatment are unknown.
Precautions
Individuals with increased risk of seizure—including those with epilepsy or a seizure disorder, a history of seizures, or a family history of epilepsy or a seizure disorder—should not receive TMS. Other people at increased risk for seizures, such as those with increased intracranial pressure due to trauma or other causes, those taking medications that increase the risk or seizures, or anyone with serious heart disease, should not receive TMS.
KEY TERMS
Analgesic —A medication to reduce or eliminate pain.
Electroconvulsive therapy (ECT) —A controversial treatment in which controlled, low-dose electrical currents are used to cause a seizure. Although rarely used today, ECT is still sometimes used in the treatment of severe depression. The benefits of ECT in the treatment of depression are temporary.
Noninvasive —A medical treatment that does not break the skin.
Tinnitus —Noise in one or both ears, including ringing, clicking, or buzzing.
The magnetic force generated by TMS will attract metallic objects and repel magnetic objects. Therefore, individuals with intracranial metallic or magnetic objects such as shrapnel or plates, screws, or clips from surgical procedures should not receive TMS unless the effects of the magnetic force on the object are known. Similarly, individuals with cardiac pacemakers, electrodes inside the heart, or implanted medication pumps should not receive TMS. Pregnant women or those who might be pregnant should not receive TMS.
Resources
BOOKS
Bezchlibnyk-Butler, Kalyna Z. and J. Joel, Jeffries, eds. Clinical Handbook of Psychotropic Drugs. Cambridge, MA: Hogrefe and Huber Publishing, 2006.
Farah, Martha J and, Todd E. Feinberg, eds. Patient-Based Approaches to Cognitive Neuroscience. 2nd ed. Cambridge, MA: MIT Press, 2005.
Lisanby, Sarah H., ed. Brain Stimulation in Psychiatric Treatment. Arlington, VA: American Psychiatric Publishing, 2004.
VandenBos, Gary R., ed. APA Dictionary of Psychology. Washington, DC: American Psychological Association, 2007.
Walsh, Vincent and Alvaro Paqscual-Leone. Transcranial Magnetic Stimulation: A Neurochronometrics of Mind. Cambridge, MA: MIT Press, 2003.
Ruth A. Wienclaw, Ph.D.