Transcranial Magnetic Stimulation
When I was at the National Institutes of Health in the early 1990s, I worked on transcranial magnetic stimulation of the brain. In Chapter 8 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I describe this technique.
8.7 Magnetic Stimulation
Since a changing magnetic field generates an induced electric field, it is possible to stimulate nerve or muscle cells without using electrodes. The advantage is that for a given induced current deep within the brain, the currents in the scalp that are induced by the magnetic field are far less than the currents that would be required for electrical stimulation. Therefore transcranial magnetic stimulation (TMS) is relatively painless…
One of the earliest investigations was reported by Barker, Jalinous and Freeston (1985). They used a solenoid in which the magnetic field changed by 2T in 110 μs to apply a stimulus to different points on a subject’s arm and skull. The stimulus made a subject’s finger twitch after the delay required for the nerve impulse to travel to the muscle.
The story of how Tony Barker invented transcranial magnetic stimulation is fascinating. You can hear about it in the above video, where John Rothwell — another early magnetic stimulation researcher — reminisces with Barker about his invention. The most interesting part of the video is when Barker describes a crucial trip he made from Sheffield (he worked at the Royal Hallamshire Hospital in Sheffield, England) to London ( The National Hospital, Queen’s Square), so he could demonstrate his device to leading neurophysiologist Pat Merton. Rothwell, also at Queen’s Square, had his brain stimulated that day, and the next day he wrote Barker asking to get a stimulator of his own. Barker’s 1985 paper in (cited in IPMB) was the first publication about magnetic stimulation of the brain. As Barker says, “like all the best papers it was one page long.”
The 15-minute video at the top of this post is well worth your time. I’ll stop writing so you can listen. Enjoy!
Originally published at http://hobbieroth.blogspot.com.