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The principles of transcranial magnetic stimulation (TMS) were established in the late 19th century experiments of Dr. David Ferrier, a Scottish neuroscientist. The prevailing view at that time was that the brain acted as a whole and no one part is responsible for a particular process. By stimulating specific parts of animal brains using an alternating current, he was able to induce the animal to move a specific limb or to move as if they have touched, smelled or heard something.
Although a much earlier experiment by Fritsch and Hitzig in 1870 showed that stimulating the brain of dogs with a direct current produced movement, Ferrier’s use of alternating current closely mimics the natural electric activity of nerve cells. Thereafter, this was used by all investigators and became the basis of TMS.
In 1896, A. D’Arsonval and A. Beer took it a step further by demonstrating that brain stimulation can be done by a magnetic field created by driving a large coil with alternating current. A volunteer experienced flashing lights and dizziness after placing his head inside a coil. However it was not until the more powerful capacitors in the 1980s allowed researchers to induce repeatable effects on the human brain. A.T. Barker et al demonstrated that placing a coil over specific parts of the human head could produce contractions of hand muscles. Since then, TMS has been used in numerous research and clinical applications.
Similar to Ferrier’s findings, investigators have used TMS to stimulate specific parts of the brain to produce tingling sensations or sounds. Furthermore, the contribution of an area of the brain to a task can be prevented by applying TMS. Thus, TMS effectively maps out which brain sites are active during a particular task and at what precise moment it is active.
It is also useful in studying a process called neural plasticity – the reorganization of brain function due to new training or disease. For example, it is common medical knowledge that the left motor cortex of the brain controls movement of the right side of the body and vice versa. If a stroke affects the left motor cortex and effectively paralyzes the patient’s right hand, patients gradually recover their right hand function. TMS studies show that the recovery is due to the unaffected right motor cortex improving its control of the muscles of both hands.
The crossover to clinical applications was not difficult to make. TMS has been successful in determining which part of the brain controls speech and language, guiding surgeons in their operations to remove brain tumors without compromising the patient’s speech or comprehension skills. Nowadays, TMS is used to treat neuropsychiatric conditions like stroke, Alzheimer’s disease and depression. Although clinical trials to support such applications are still scarce, this makes for an exciting area of research for years to come.
At the Fort Worth TMS center, dr Diana Ghelber, a board certified psychiatrist, trained in the use of TMS for depression, can help you deal with depression, even when medications did not help.
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