Study explains why healthy individuals don't get tremors
1 June 2010
Mild tremor can be a feature of daily life even in healthy individuals, especially when nervous, tired or hungry. However, around one million people in the UK suffer from shakes and tremors as a symptom of nervous diseases, such as Parkinson's, multiple sclerosis and essential tremor. Essential tremor is common in old age, though younger people can also be affected, and in severe cases it can leave patients unable to walk unaided.
Now, Professor Stuart Baker and colleagues at Newcastle University have made a discovery that could help to explain what causes these tremors.
"Instead of looking at why people suffer from tremors, we started to look at why most people don't suffer from them," explains Professor Baker. "The brain waves from the parts of the brain controlling movement work at 10 cycles per second, so really, everyone should have a tremor at that frequency. In fact we do, but for most of us - most of the time - tremor is so small as to be hardly noticeable."
In a study published in the 'Proceedings of the National Academy of Sciences', researchers taught macaque monkeys to move their index finger slowly backwards and forwards. This exacerbated the natural minor tremors that both primates and humans experience. The team then used sensors to record the activity of nerve cells from the brain and the spinal cord as the animals moved.
The brain and spinal cord both showed rhythmic activity at the same frequency as the tremor. However, crucially, the signals in the spinal cord were out of phase with those in the brain. In other words, when the wave in the brain was at its peak, the wave in the spinal cord was at its lowest point and vice versa. This meant that the two waves in effect cancelled one another out, reducing the size of the tremor.
Professor Baker believes that the system controlling nerve signals in the spinal cord may malfunction in some diseases. The ability of the spinal cord to counteract the brain's activity then breaks down, leading to tremor.
In other diseases, the problem occurs in the brain: particular brain regions produce abnormally high oscillations. However, even in these cases, the system identified by Professor Baker and colleagues will reduce tremors, making the symptoms much less severe than they would otherwise be.
"Understanding more about how the spinal controller works could open the way to adjusting it to work better, reducing the levels of tremors patients suffer and improving their lives," he says.
Image: Model showing a network of nerve cells. Credit: Wellcome Images
Reference
Williams ER et al. Spinal interneuron circuits reduce approximately 10-Hz movement discontinuities by phase cancellation. Proc Natl Acad Sci USA 2010.
