Fri July 25/2008
Fri July 25/2008 |
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Repetitive Transcranial Magnetic Stimulation (rTMS)What is Repetitive Transcranial Magnetic Stimulation? Repetitive Transcranial Magnetic Stimulation (rTMS) is a procedure that uses a pulsed magnetic field to influence electrical activity in the brain. In this a brief current pulses is passed through a coil or wire that is shaped like a Figure 8 creates the magnetic field. To allow the magnetic field to focus on certain areas of the brain, the coil of wire is enclosed in plastic and held close to the brain. This magnetic field is capable of penetrating the skull safely and painlessly to induce a current in certain brain cells. The stimulation is called repetitive because it is delivered at regular intervals. How is rTMS administered? Because rTMS is an outpatient, non-evasive procedure, no hospitalization or anesthesia is required. It can also be administered in a clinical setting by a trained technician under the supervision of a physician instead of in the outpatient department of a hospital. In order to administer the magnetic stimulation, a figure eight coil of wire enclosed in plastic is held over the scalp. A motor-invoked potential in the abductor policis brevis or thumb muscle will determine the intensity of the stimulus that will be delivered. Headaches and unwanted noise may be experienced based on the intensity of the stimulus. Earplugs are worn to reduce the noise, and headaches usually disappear within a few hours or following a dose of Tylenol. Why is rTMS used for depression? Repetitive Transcranial Magnetic Stimulation can target areas of the brain that are believed to be target areas of depression. In addition, it has the potential to selectively modulate or change activity in the areas of the brain that affect depression and are involving with the determination of mood. One of the determining factors in depression is a decrease in the levels of activity in the prefrontal cortex of the brain, particularly the left side of the brain. The dorsolateral prefrontal cortex (DLPFC) located just a few inches above the temple and beneath the skull is the area that is stimulated for treating depression. This area is readily accessible to the magnetic field and is highly interconnected with other structures that play a role in mood modulations and major depression. Repetitive Transcranial Magnetic Stimulation treats depression by inducing a current into the DLPFC with stimulation by a magnetic field. According to several studies, rTMS down regulates beta adrenoreceptors and increases the levels of dopamine and serotonin. Additionally, rTMS can alter activity in other remote areas of the brain structure even though they are not directly accessible to the rTMS coil. A process of focal cortial stimulation does this, and some of these remote brain structures are also believe to be linked to depression. It is through this focal intervention that rTMS is able to alter the activity in these small areas of the brain directly and indirectly. The indirect stimulation occurs through a process called trans-synaptic effects, meaning that the accessible areas of the brain described above are directly stimulated by the magnetic field first. The inaccessible areas of the brain are then stimulated, resulting in an indirect stimulation. When was rTMS developed? Repetitive Transcranial Magnetic Stimulation was designed in the mid 1980’s as a neurodiagnostic tool. It was also used to study nerve fibres and create a function map of the brain in clinical neurophysiology. Through technical developments in the devices used to administer the magnetic stimulation, it became possible to apply more and faster stimuli to specific areas of the brain. By the early 1990’s rTMS was beginning to be used to treat depression. Numerous clinical trials were conducted in the 1990’s, and research has been ongoing around the world for over ten years.
Can rTMS be used for other illnesses? According to current research, rTMS has a valuable therapeutic potential to treat other illnesses and disorders other than depression. Because of its capacity to selectively increase or decrease the excitability of neurons in certain areas of the brain, it mail hold promise in the treatment of other illnesses. Recent studies have shown that rTMS shows promise in the treatment of Parkinson’s disease, Schizophrenia, Bipolar Disorders and some other mood disorders. Further research is still being conducted to determine the overall effectiveness in treating these conditions. Only the future will show how far and to what degree rTMS will be beneficial in treating other mood-altering disorders, but for now, we can only accept that research and case studies are still in the process. |
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