Repetitive transcranial magnetic stimulation (rTMS) is a new technology that is showing promise as a treatment for depression.
Transcranial magnetic stimulation (TMS) is a technique for gently stimulating the brain. It utilizes a specialized electromagnet placed on the patient’s scalp that generates short magnetic pulses, roughly the strength of an MRI scanner’s magnetic field but much more focused. The magnetic pulses pass easily through the skull just like the MRI scanner fields do, but because they are short pulses and not a static field, they can stimulate the underlying cerebral cortex (brain). Low frequency (once per second) TMS has been shown to induce reductions in brain activation while stimulation at higher frequencies (> 5 pulses per second) has been shown to increase brain activation. It has also been shown that these changes can last for periods of time after stimulation is stopped. TMS was first developed in 1985, and has been studied significantly since 1995.
How Transcranial magnetic stimulation works?
The exact details of how TMS functions are still being explored, but the MIT Technology Review listed some potential mechanisms:
A doctor typically holds a powerful magnet over the frontal regions of the patient’s skull and delivers magnetic pulses for a few minutes a day, over the course of a few weeks. The treatment alters the biochemistry and firing patterns of neurons in the cortex, the part of the brain nearest the surface. Preliminary research indicates that the treatment affects gene activity, levels of neurotransmitters like serotonin and dopamine, and the formation of proteins important for cellular signaling-any of which could play a role in alleviating depression. What’s more, magnetic stimulation seems to affect several interconnected brain regions, starting in the cortex and moving to the deep brain, where new cell growth may be important in regulating moods.
In practice, TMS and rTMS are able to influence many brain functions, including movement, visual perception, memory, reaction time, speech and mood. The effects produced are genuine but temporary, lasting only a short time after actual stimulation has stopped.
How many times do you need to receive TMS?
Research protocols vary in the treatment duration, but most require at least two weeks of daily stimulation given five times per week, some require up to 6 weeks.
Generally, TMS appears to be free from harmful effects. Research using animals and human volunteers has showed little effect on the body in general as a result of stimulation, and examination of brain tissue submitted to thousands of TMS pulses has shown no detectable structural changes. It is possible in unusual circumstances to trigger a seizure in normal patients, but a set of guidelines which virtually eliminate this risk are available. Research continues, but TMS is certainly free of obvious side-effects like those of electro-convulsive therapy (ECT), which still makes quite an impact on patients despite refinements in technique.
TMS shows promise as a novel antidepressant treatment. Systematic and large-scale studies are needed to identify patient populations most likely to benefit and treatment parameters most likely to produce success. In addition to its potential clinical role, TMS promises to provide insights into the pathophysiology of depression through research designs in which the ability of TMS to alter brain activity is coupled with functional neuroimaging.