TMS – A Promising Tool for Treating the Brain

In my last post I went through the early history of the technology behind TMS – transcranial magnetic stimulation. Thanks to Dr. Anthony Barker, by the beginning of the 1990s, we had for the first time a way of directly altering brain activity, from outside the (intact!) skull, in a way that was harmless and non-invasive.

Researchers immediately took to TMS, because it opened up a whole new avenue of scientific inquiry. For the first time, they could explore the functions of particular brain locations by adjusting their activity in real time, safely and reversibly. For example, they could temporarily “knock out” the part of the right hemisphere that facilitates awareness of objects in the left half of people’s visual field, and see if the people did indeed start failing to detect objects appearing on their left. (Hint: They did.) Or, they could stimulate the speech articulation areas of the brain while people were talking, and observe whether the stimulation altered or disrupted the flow of their speech. They managed to do that too! Check out this video, in which a gentleman takes a TMS coil and stimulates his own left-hemisphere articulatory speech centre (called “Broca’s Area”) while talking:

This was all a real boon for scientists, because up to that point they had had to rely heavily on research subjects with various brain injuries to try to figure out which parts of the brain were involved in which functions.

Two further insights into the effects of TMS had to emerge in order for it to become a useful clinical tool. First, it didn’t take long for researchers to figure out that different arrangements of the timing of the magnetic pulses had different effects on the brain. Some pulse timings (generally, faster-paced pulses, such as 10 or 20 pulses per second) have an excitatory effect, increasing the brain’s activity at the location where the pulses were applied. Other pulse timings (generally, more slowly-paced pulses, e.g., one pulse per second) have an inhibitory effect, reducing the brain’s activity – almost like slowing the brain down.

Second, researchers figured out that although TMS pulses’ effects were always transient and temporary when only a few were delivered, the effects could be made more long-lasting when the brain was stimulated with lengthy “trains” of many pulses in a row. The reasons for this are still being studied, but what is now clear is that longer runs of TMS pulses delivered multiple times induce the brain to make changes to its own internal wiring (sometimes called neuroplastic changes), creating effects that last well beyond the end of the actual stimulation. This was obviously necessary if TMS was to become useful as a way of making real-life changes that would last.

Supplied with these two insights, scientists were now in a position to explore how TMS could be useful as a treatment tool. They could up- or down-regulate the brain’s activity, in any location close enough to the scalp to be reached by the coil’s magnetic field. So they could affect all kinds of different brain functions, from sensory experience to muscle control to short-term memory, and by repeatedly delivering long trains of pulses, these changes could leave the brain functioning differently after the stimulation had ceased.

The first studies of repetitive TMS as a treatment for depression were published in the 1990s. Dr. Mark S. George and his colleagues were the first to find that excitatory TMS, applied to the brain’s left frontal lobe, had a lasting depression-lifting effect. That initial observation has held up remarkably well over 30 years and thousands upon thousands of patients: although the exact stimulation site and the arrangement of the magnetic pulses have seen some adjustments, that same location on the left frontal lobe remains the most commonly targeted stimulation site for depression to this very day, including for many of the patients we treat at Breakwater Neuro.

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