Single unit “pauser” characteristics of the globus pallidus pars externa distinguish primary dystonia from secondary dystonia and Parkinson's disease

The presence of high frequency discharge neurons with long periods of silence or “pauses” in the globus pallidus pars externa (GPe) is a unique identifying feature of this nucleus. Prior studies have demonstrated that pause characteristics reflect synaptic inputs into GPe. We hypothesized that GPe pause characteristics should distinguish movement disorders whose basal ganglia network abnormalities are different. We examined pause characteristics in 224 GPe units in patients with primary generalized dystonia, Parkinson's disease (PD), and secondary dystonia, undergoing single unit microelectrode recording for DBS placement in the awake state. Pauses in neuronal discharge were identified using the Poisson surprise method. Mean pause length in primary dystonia (606.8373.3) was higher than in PD (557.4366.6) (p < 0.05). Interpause interval (IPI) was lower in primary dystonia (2331.63874.1) than PD (3646.45894.5) (p < 0.01), and mean pause frequency was higher in primary dystonia (0.140.10) than PD (0.070.12) (p < 0.01). Comparison of pause characteristics in primary versus secondary generalized dystonia revealed a significantly longer mean pause length in primary (606.8373.3) than in secondary dystonia (495.6236.5) (p < 0.01). IPI was shorter in primary (2331.6 ± 3874.1) than in secondary dystonia (3484.5 ± 3981.6) (p < 0.01). The results show that pause characteristics recorded in the awake human GPe distinguish primary dystonia from Parkinson's disease and secondary dystonia. The differences may reflect increased phasic input from striatal D2 receptor positive cells in primary dystonia, and are consistent with a recent model proposing that GPe provides capacity scaling for cortical input.