Dopamine dependency of oscillations between subthalamic nucleus and pallidum in Parkinson's disease

The extent of synchronization within and between the nuclei of the basal ga nglia is unknown in Parkinson's disease. The question is an important one b ecause synchronization will increase postsynaptic efficacy at subsequent pr ojection targets. We simultaneously recorded local potentials (LPs) from th e globus pallidus interna (GPi) and subthalamic nucleus (STN) in four awake patients after neurosurgery for Parkinson's disease. Nuclei from both side s were recorded in two patients so that a total of six ipsilateral GPi-STN LP recordings were made. Without medication, the power within and the coher ence between the GPi and STN was dominated by activity with a frequency <30 Hz. Treatment with the dopamine precursor levodopa reduced the low-frequen cy activity and resulted in a new peak at <similar to>70 Hz. This was evide nt in the power spectrum from STN and GPi and in the coherence between thes e nuclei. The phase relationship between the nuclei varied in a complex man ner according to frequency band and the presence of exogenous dopaminergic stimulation. Synchronization of activity does occur between pallidum and ST N, and its pattern is critically dependent on the level of dopaminergic act ivity.