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Transcranial magnetic stimulation (TMS) occurs when a rapid release of electric pulses to an insulated coil creates a magnetic field, thus generating an electric current that passes through the scalp and bone to cause brain stimulation. The induced current is weak and brief. However, it can stimulate nerve cells, leading to a specific response like muscle twitching.
A TMS machine basically consists of a capacitor, which generates the electrical current and a coil. The capacitor is charged for a few seconds then the stored energy is released into the coil as a single or multiple pulses. Most researches and treatments use machines that generate rapid, biphasic pulses as these lead to a longer stimulating effect, allowing for lower currents to be used, less recharging time and less energy consumption. The coil type to be used depends on the objective of the treatment. A simple round coil is used when one wishes to stimulate a larger portion of the brain whereas a figure-of-eight coil would give a more concentrated stimulation.
During the TMS procedure, the patient is conscious and seated comfortably. A cap may be worn to mark the coil’s position over the patient’s head. The first step is to map out the location of the motor cortex, the area of the brain responsible for muscle control. This is done by slowly moving the coil over the scalp while delivering electrical pulses until a response is noted, usually the contraction of the thumb. Afterwards, the lowest stimulation intensity that achieves a muscle contraction is determined. This would serve as the intensity level if TMS is used for treatment.
For treatment purposes, it is important to determine the site where TMS should be applied and this depends on the patient’s condition. If the patient suffered a stroke with paralysis of the right arm and leg, stimulation is delivered to the left motor cortex as this controls movement on the right side of the body. In this case, the stimulation site is located by moving the coil over the left side of the head and monitoring for muscle twitching on the right side of the body.
If the response to TMS is not readily seen like the alleviation of mood symptoms in depressed patients, the coil placement is based on the known anatomic location of the part of the brain responsible for mood. Both methods are not precise and nowadays, coil placement can be individualized with the help of the magnetic resonance imaging (MRI).
TMS is non-invasive and causes minimal pain or discomfort to the patients. The most serious adverse effect are seizures, especially if TMS occurs at an intensity level that is close to producing movements of the limbs. Most practitioners would not use TMS if the patient has a personal or family history of epilepsy. Temporary memory loss immediately after the procedure has also been reported.
As a research tool, TMS can explain what areas of the brain are involved in specific processes and when they are involved. As a form of treatment, TMS has been used to treat disorders such as stroke, Parkinson’s and depression. However, its mechanisms of action have yet to be elucidated.
Dr Diana Ghelber, at the Fort Worth TMS center, is a board certified psychiatrist trained in the use of TMS (transcranial magnetic stimulation) in patients with depression.
If you struggle with depression, and medications did not offer you the improvement you expected, contact Dr Ghelber at the Fort Worth (TX) TMS center to check if the transcranial magnetic stimulation is the right step for you!
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