A substantial body of work within the last decade has demonstrated that there is a variety of oscillatory phenomena that occur in the basal ganglia and in associated regions of the thalamus and cortex. Most of the earlier studies focused on recordings in rodents and primates. More recently, significant advances have been made in this field of research through the analysis of basal ganglia field potentials recorded from implanted deep brain stimulation electrodes in the basal ganglia of human patients with Parkinson's disease and other disorders. It now appears that oscillatory activity may play a significant role in the pathogenesis of these diseases. The most significant finding is that in Parkinson's disease synchronized oscillatory activity in the 10- to 35-Hz band (often termed "beta-band") is prevalent in the basal ganglia-thalamocortical circuits, and that such activity can be reduced by dopaminergic treatments. The entrainment of large portions of these circuits may disrupt information processing in them and may lead to parkinsonian akinesia (and perhaps tremor). Although less firmly established than the role of oscillations in movement disorders, oscillatory activities at higher frequencies may also be a component of normal basal ganglia physiology.

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Dopamine depletion in Parkinson's disease (PD) alters the neuronal activity in basal ganglia circuits. Characterizing these changes in network activity is an important step in understanding the disease and how therapies mitigate symptoms. Non-linear analysis methods can complement the traditional description of neuronal firing characteristics. Here we examine the entropy of subthalamic neurons in PD patients undergoing stereotactic surgery for deep brain stimulation (DBS). The activity of 8 neurons was recorded prior to, during, and following systemic administration of the dopamine agonist apomorphine at clinically effective doses. Apomorphine induced a decrease in entropy measured in the inter-spike intervals of subthalamic neurons in 6 of the 8 neurons. This is the first report that antiparkinsonian drugs affect non-linear features of neuronal firing in the basal ganglia of parkinsonian patients. Keywords nonlinear; firing pattern; interspike intervalThe motor signs and symptoms of Parkinson's disease (PD) are in large part caused by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc), and the resultant loss of dopamine throughout the basal ganglia. As a consequence, neuronal activity is altered throughout the basal ganglia in general, including the subthalamic nucleus (STN).Changes in STN neuron activity have been described in both rodents and non-human primates after dopamine depletion. There is a large body of evidence suggesting that dopamine depletion