Oscillatory activity in the basal ganglia--relationship to normal physiology and pathophysiology

There is mounting evidence that rhythmic brain oscillatory rhythms play important roles in processes such as perception, motor action and conscious experience, and that disruption or increases of activity in various oscillatory networks may be an important factor in mediating some of the symptoms associated with neurological diseases (Llinas et al ., 1999; Bevan et al ., 2002). Rhythmic brain activity is of course well known from the EEG, where several different frequency ranges of oscillatory activity have been well characterized, the best known being the alpha rhythm that is generally observed when the eyes are closed. The oscillatory activity is usually identified and studied in cortical local field potentials (LFPs) and EEG, and reflects local rhythmic synchronized subthreshold activity in presynaptic terminals and the postsynaptic neurons. However, synchronized oscillatory neuronal firing supra‐thershold (spike) activity can also be recorded and is likely to be related directly to the LFP oscillations. Oscillatory rhythms can be widespread, and rhythmic activity of the same frequency frequently can be observed to occur over wide cortical areas and even in the LFPs recorded in subcortical regions. Oscillatory activity in the basal ganglia (BG) has attracted a great deal of interest in the past few years as it is thought to be important in both the normal functioning of the system and the pathophysiology of Parkinson’s disease (see review by Bevan et al ., 2002). Studies of neuronal firing in …