Subthalamic nucleus neuronal firing rate increases with Parkinson's disease progression

Parkinson's disease is a neurodegenerative disorder characterized by progressive loss of dopaminergic cells in the central nervous system, in particular the substantia nigra, resulting in an unrelenting loss of motor and nonmotor function. Animal models of Parkinson's disease reveal hyperactive neurons in the subthalamic nucleus that have increased firing rates and bursting activity compared with controls. Although subthalamic nucleus activity has been characterized in patients with advanced-stage Parkinson's disease, it has not been described in patients with early-stage Parkinson's disease. Here we present the results of subthalamic nucleus neuronal recordings from patients with early-stage Parkinson's disease (Hoehn and Yahr stage II) enrolled in an ongoing clinical trial compared with recordings from age- and sex-matched patients with advanced Parkinson's disease. Subthalamic nucleus neurons had a significantly lower firing rate in early versus advanced Parkinson's disease (28.7 vs 36.3 Hz; P<.01). The overall activity of the subthalamic nucleus was also significantly lower in early versus late Parkinson's disease, as measured by background neuronal noise (12.4 vs 14.0 mV; P<.05). No significant difference was identified between groups in the bursting or variability of neuronal firing in the subthalamic nucleus, as measured by a burst index or the interspike interval coefficient of variability. The results suggest that neuronal firing in the subthalamic nucleus increases with Parkinson's disease progression.