Granger causality supports abnormal functional connectivity of beta oscillations in the dorsolateral striatum and substantia nigra pars reticulata in hemiparkinsonian rats.

Synchronized oscillatory neuronal activity in the beta frequency range has been reported in the basal ganglia (BG) of patients with Parkinson disease (PD) and PD animal models. The coherent abnormal oscillatory activities in the dorsolateral striatum (dStr) and substantia nigra pars reticulata (SNr) that accompany parkinsonian states have not been resolved. In this study, we recorded local field potentials (LFPs) in the dStr and SNr of 6-hydroxydopamine (6-OHDA)-induced dopamine (DA)-lesioned rats in an awake, resting state. Analyses of power spectral density and coherence data demonstrated augmented LFP power in the 24-36-Hz (high beta) range in both the dStr and SNr together with increased dStr-SNr coherence in the 24-36-Hz range, relative to sham controls; both effects were reversed by levodopa (L-dopa) treatment. Partial Granger causality analysis revealed a dStr→SNr propagation directionality of these beta oscillations. These findings support the involvement of increased synchronization of high beta activity in the dStr and the SNr, and suggest that dorsolateral striatal activity plays a determinant role in leading the coherent activity with the SNr in the development of parkinsonian pathophysiology.