Newcastle University

It is known that the neurons which control movement and which are found within the primary motor cortex area of the brain (area M1) commonly show synchronous oscillations in activity that occur at frequencies of around 10 and 20 Hz.  Furthermore, recordings of the electromyogram (EMG) from muscles of the forearm and hand which these neurons control  show similar oscillations during a sustained contraction, such as a grip movement.  However, whilst the oscillations in the brain and muscles which are happening at around 20 Hz occur in an apparently linked manner (i.e. they are phase-locked or ‘coherent’), no such ‘corticomuscular coherence’ occurs for the oscillations that occur at 10 Hz. Professor Stuart Baker has proposed that one reason for this is that at some point along the pathway from the brain to the muscles there is a mechanism (a neural filter) that cancels out this particular frequency of oscillatory activity. He has argued that the purpose of such filtering is to reduce the amount of tremor that occurs in the muscle, thereby improving fine movement.  In this study conducted with Dr Liz Williams, they used a computer model of the neural pathways controlling movement to examine what effect inhibitory feedback within the spinal cord would have on the transmission of oscillatory activity.  Such ‘recurrent inhibition’ is known to occur through a specific class of neuron called the Renshaw cell. The results clearly demonstrated that recurrent inhibition plays an important role in reducing 10 Hz oscillations in muscle, thereby decreasing tremor amplitude.  However, their results also suggest that this inhibition does not account for all the filtering and other mechanisms probably act simultaneously to eliminate tremor.  Professor Baker hopes that by understanding these mechanisms it is possible to determine why tremor develops in certain pathological conditions (such as Parkinson’s Disease) and this may help with developing new treatments.

Renshaw cell recurrent inhibition improves physiological tremor by reducing corticomuscular coupling at 10 Hz. Williams ER, Baker SN (2009) Journal of Neuroscience 29:6616-6624 (PubMed abstract http://www.ncbi.nlm.nih.gov/pubmed/19458232)