Neural rhythms in Parkinson’s disease

Abstract

Neurologists should take brain rhythms seriously. Classical neurophysiology has focused on the encoding of information through changes in the firing rate of neurones, the salience of a stimulus or initiation of a motor response being accompanied by increases or decreases in neuronal activity. Yet when networks of neurones interact the result is often rhythmic activity within defined frequency ranges that can engage in temporal synchronization and de‐synchronization. Neurologists are predisposed to consider all rhythmicity as pathological. After all, in our working lives we diagnose essential tremor and the tremor of Parkinson’s disease and many of our concepts of diseases such as epilepsy are bound up with ideas of widespread rhythmic synchronization of neural elements resulting in loss of consciousness and violent involuntary movement. Over recent years a more sophisticated appreciation of neural rhythmicity and temporal synchronization has emerged. Neurophysiologists can now record simultaneously from networks of neurones in cortical and sub‐cortical structures of humans and animals. We are beginning to understand that brain rhythms, their synchronization and de‐synchronization, form an important and possibly fundamental part of the orchestration of perception, motor action and conscious experience (Singer, 1993; Farmer, 1998) and that disruption of oscillation and/or temporal synchronization may be a fundamental mechanism of neurological disease. Levy and colleagues in this issue of Brain (Levy et al ., 2002) report the results of sophisticated micro‐ and macro‐electrode recordings from sub‐thalamic nucleus (STN) in conscious patients undergoing neurosurgical treatment for advanced Parkinson’s disease. Their data consists of action potentials recorded from micro‐electrodes and local field potentials recorded using macro‐electrodes. Using Fourier analysis they have identified the dominant frequencies of oscillatory activity in action potential spike trains and local field potentials. Application of coherence analysis to such data …