In the latest issue of the journal Neuron, Professor John Rothwell and colleagues from UCL's Institute of Neurology discovered ways to improve TMS to produce effects on the brain that last for more than an hour after only 40 seconds of stimulation. Longer-lasting effects will enable scientists to use TMS to modify brain activity in conditions ranging from depression to brain damage.
TMS stimulates the brain via a magnetic coil held outside the skull which can be moved over different parts of the brain. The magnetic fields created by the coil induce tiny electrical currents inside the skull that alter the activity of neural pathways, stimulating or inhibiting activity in parts of the brain.
The technique has been used predominantly as a research tool to study how the healthy brain reacts to injury or damage but scientists have recently started to explore its possibilities as a treatment for depression, epilepsy, stroke and Parkinson's disease. A handful of studies have already shown potential therapeutic benefits from TMS.
The advantage of TMS is that it is non-invasive and does not require a patient to be hospitalized i.e. the treatment can be given in an out-patient clinic. However, the drawback in the past has been that TMS led to only transient neurological effects which rarely lasted longer than 30 minutes. The new method pioneered by the UCL team holds promise that much longer lasting and more powerful effects can be produced.
Professor Rothwell's team adapted the technique by testing different patterns of repetitive magnetic pulses to the scalps of volunteers, delivered over a period of 20 to 190 seconds. The pulses were aimed at the motor cortex that controls muscle response, because effects on the motor cortex can be objectively measured by recording the amount of electrical muscle response to stimulation.
The researchers positioned the magnetic coil over the motor cortex area that controls hand movement and measured the amount of muscle response in a small muscle in the subjects' hands. They discovered that the excitatory effect of TMS builds up rapidly, within about a second, while the inhibitory effect builds up within several seconds. Thus, by adjusting the length of stimulation, they could choose between stimulating or suppressive effects on the brain.
The team were able to produce rapid, consistent and controllable changes in the motor cortex area, lasting double the amount of time of conventional TMS. Initial tests performed to assess the safety of TMS showed that there were no long-lasting or side effects from these stimulations.
Professor Rothwell says: "Now that we have improved the technique, we can use it to explore whether stimulation of damaged areas in stroke patients' brains can help speed up their recovery. Alternatively, it may be that in some patients the 'healthy' side of the brain interferes with recovery by the damaged side, so that another approach would be to reduce its activity and stop it competing for control."
Rothwell's team are also investigating the possibility of applying the method to patients with Parkinson's disease or dystonia.