Pallidal activity in Parkinson's disease patients with intraoperative dyskinesias.

OBJECTIVE

We aimed to investigate the differences in activity of globus pallidus externus (GPe) and internus (GPi) in Parkinson's disease (PD) following levodopa uptake in comparison with the unmedicated state.

METHODS

We compared single unit activity of the GPe and the GPi of two parkinsonian patients who exhibited levodopa-induced dyskinesias (LID) during deep brain stimulation surgeries with three unmedicated patients with comparable levodopa response. We focused on discharge rates, firing patterns and oscillatory properties of the neurons.

RESULTS

We observed that the majority of the GPi neurons fired less frequently and regularly following levodopa administration, but no uniform differences were found in the GPe. We found no units oscillating in low beta (12-20 Hz) in either state, but several GPi cells demonstrated oscillatory discharge in 4-5 Hz and 20-30 Hz on medication.

CONCLUSIONS

Our findings suggest that the GPi is more uniformly responsive to levodopa than the GPe. They also point towards the plausible need for revisiting the model of beta oscillations' emergence as a result of synchronized bursting in the STN-GPe-GPi network.

SIGNIFICANCE: Our study investigates the effect of dopamine-replacement therapy with levodopa on the GPe and GPi at the single-cell level, contributing to understanding the PD pathophysiology.