By Andy Ho

A MEDICAL malpractice suit recently resolved in the courts here involved a well-known neurologist who used an unusual therapy called repetitive transuranic magnetic stimulation (TMS).

As the name implies, this is a non-invasive technology that uses magnetic forces to stimulate the human brain through the skull. What are actually used are electromagnetic coils, something first devised by British physicist Michael Faraday.

In 1831, Faraday used a battery to run an electric current through a small coil, which created a magnetic field around it. The small coil was placed inside a larger coil which was not connected to any battery, so it had no electricity running through it. However, when the small coil was moved in and out of the larger coil, the former's magnetic field was shown to induce an electric current in the latter.

This principle of 'electromagnetic induction' is that which lies behind the way today's electric generators work. By the same principle, running electric pulses through TMS coils - which are held over a patient's head - induces a pulsating magnetic field, which can penetrate the intact skull to induce a pulsating electric field inside the brain itself.

How is that possible since there are no coils of electric wires inside the brain? But neurons or long nerve cells in the brain do have electric charges (ions) stored on both sides of their cell membranes. What the TMS coils' pulsating magnetic field does is to alter the flow of ions in and out of these neuron cell membranes. This translates into changes in nerve impulses, which are basically just electric signals.