A New Approach For Calming Parkinson's Tremors

Many neuroscientists believe that pathological brain rhythms, for example in Parkinson's disease and in epilepsy, arise from an abnormal synchronization of many thousands of nerve cells (neurons). This physical mechanism appears in many physical and biological systems. For example, it enables fireflies to light up in unison.

Sometimes, synchrony is desirable, for instance, when the cells of the heart's main pacemaker (the sino-atrial node) fire all together to stimulate heart contraction.

But in many cases synchrony is harmful. London's Millennium Bridge, which swayed undesirably shortly after it opened in 2000, provides a useful example. Hundreds of pedestrians subconsciously synchronized their pace to the bridge's sideways, left-to-right swaying motions. The bridge oscillations, driven by pedestrians, became dangerously large, and the walkway had to be closed for reconstruction.

In the case of a Parkinson's tremor one also needs to suppress the synchronous oscillations of nerve cells, but one can hardly apply the methods used by engineers for the Millennium Bridge. Thus, researchers need a technique to control the collective synchrony of neurons.

Now, a paper suggests a new approach: one would measure the collective rhythm of nerve cells and, after some delay, electrically
"feed back" this rhythm into the population of nerve cells. Adjusting the delay time and the amplification in the feedback loop, the researchers in principle could either suppress or enhance the collective rhythm.

The researchers (Michael Rosenblum, mros@agnld.uni-potsdam.de, and Arkady Pikovsky, pikovsky@stat.physik.uni-potsdam.de, University of Potsdam, Germany) have tested this idea in simulations that employ mathematical models of neuron populations.

The researchers believe the scheme might be used, in particular, for suppressing Parkinson's tremors by means of the emerging medical technique, called Deep Brain Stimulation, that enables intervention with the use of implanted microelectrodes.

In principle, medical doctors could use an implanted electrode to measure electrical activity of the brain area and stimulate the nerve-cell population via a second electrode with the delayed signal. The advantage of this approach is that individual neurons are not much affected and continue to function, while the pathological collective Parkinsonian rhythm is suppressed noninvasively. (Rosenblum and Pikovsky, Physical Review Letters, upcoming.)