magnetic stimulation (TMS), in which the brain is stimulated using a
magnetic coil held outside the skull, has shown, according to
researchers, some promise in both studying the brain and in treating
disorders such as depression, epilepsy and Parkinson's disease.
In the latest issue of the journal Neuron, Professor John Rothwell and colleagues from University College London'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.
magnetic fields produced by TMS induce tiny electrical currents inside
the skull that alter the activity of neural pathways. Longer-lasting
effects will enable scientists to use TMS to modify brain activity in
conditions ranging from depression to brain damage.
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
various conditions. A handful of studies have already shown potential
therapeutic benefits from TMS.
advantage of TMS is that it is non-invasive and does not require a
patient to be hospitalised (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
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 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.
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 side effects from these stimulations.
Professor Rothwell said:
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."