Analyzing Local Field Potentials in the healthy basal ganglia under Deep Brain Stimulation

High frequency Deep Brain Stimulation in the Sub-Thalamic Nucleus is a clinically recognized therapy for the treatment of motor disorders in Parkinson´s Disease. Sub-thalamic Nucleus (STN) is a small lens-shaped nucleus in the brain where it is a part of the basal ganglia system and is currently thought to play a prominent role in Parkinson´s Disease (Obeso et al., 1997). STN is the typical stimulation target in patients with symptoms like tremor and motor skills, typical in Parkinson´s disease. The underlying mechanisms of Deep Brain Stimulation and how it impacts neighboring nuclei, however, are not yet completely understood and this is the reason because Deep Brain Stimulation is still debated. Electrophysiological data has been collected in Parkinson´s Disease patients and primates to better understand the impact of Deep Brain Stimulation(DBS) on Sub-thalamic Nucleus and the entire Basal Ganglia motor circuit. We use single unit recordings from Globus Pallidus, both pars interna and externa segments in Basal Ganglia (GPi and GPe respectively), in a normal primate before and after DBS to reconstruct Local Field Potentials in the region. The aim of this paper is to understand, via system identification techniques, how GPe activity and the DBS signal applied to Sub-thalamic Nucleus influence GPi activity (see Fig 1 and 2), in order to clarify the impact of DBS on Basal Ganglia nuclei (in particular on GPi) analyzing Local Field Potentials. Our models suggest that when no stimulation is applied, the GPe has an inhibitory effect on GPi with a 2 ms delay on Local Field Potentials (LFPs), as is the case for single unit neuronal activity (4-5 ms delay in this instance). On the other hand, when DBS is ON the models suggest that stimulation has a dominant effect on GPi LFPs which masks the inhibitory effects of GPe.