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Transcranial magnetic stimulation (TMS)


Transcranial magnetic stimulation was first developed by Dr Anthony Barker and his colleagues at the University of Sheffield (UK) in the 1980s. The basic premise of TMS is that the brain operates using electric signals, and it's possible to alter the way the brain works by altering the electrical environment. Standard equipment consists of something to generate an electromagnetic signal at a specific frequency, and a coil to focus that magnetic field on specific brain regions.

Transcranial magnetic stimulation (TMS) utilizes an electromagnet placed on the scalp that generates magnetic field pulses roughly the strength of an MRI scan. The magnetic pulses pass readily through the skull and stimulate the underlying cerebral cortex.

How Transcranial magnetic stimulation works?

TMS works on principals of electrical current established in the last few centuries. In 1831, Faraday discovered that a rapidly changing magnetic field can induce electrical current in a nearby conductor. In 1985 this principle was used to induce twitches in humans' arm and leg muscles.

The magnetic fields used in TMS are produced by passing current through a hand-held coil, whose shape determines the properties and size of the field. The coil is driven by a machine which switches the large current necessary in a very precise and controlled way, at rates up to 50 cycles per second in rTMS (Repetitive transcranial magnetic stimulation). The coil is held on the scalp - no actual contact is necessary - and the magnetic field passes through the skull and into the brain. Small induced currents can then make brain areas below the coil more or less active, depending on the settings used.

A related registration and tracking application is the generation of functional brain mapping using a trans-cranial magnetic stimulation device. This coil generates magnetic field impulses which stimulate underlying nerve cells in a focused volume. By measuring responses to the stimulations and tracking the position of the coil relative to the MR scan we generate functional maps of the brain in a low-cost, non-invasive, and accurate manner.

Transcranial magnetic stimulation (tms) for depression and other mental disorders

At first scientists used TMS mainly as a research tool to gain insights into how the brain works. But in recent years, scientists refined the strategy and found evidence that it can change brain activity and sometimes alleviate depression. Many mental illnesses can be demonstrated to stem from the abnormal behaviour of particular brain regions, in much the same way that diabetes is the result of malfunctioning cells in the pancreas. It is believed that some mental disorders are the result of nerve cells being over- or under-excitable (in other words, it is too easy or too difficult for them to "fire" and work properly). In this context, successful psychiatric treatment is achieved by modifying these cells' behaviour. The range of effects produced by TMS are a clear indication of its potential to work in this way.

TMS is considered an inexact technology, but researchers have just begun to explore its potential in neuroscience.

TMS (Transcranial magnetic stimulation) and rTMS (Repetitive transcranial magnetic stimulation)

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