Neuronal firing before and after burst discharges in the monkey basal ganglia is predictably patterned in the normal state and altered in parkinsonism

Abstract

It is known that burst discharges in basal ganglia neurons are more common in parkinsonism than under normal conditions, but changes in the structure of burst or peri-burst epochs have not been reported. In this study, the temporal structure of bursts and the timing of neuronal discharges that precede or follow them were examined in neuronal spike trains recorded in the subthalamic nucleus (STN) and the external and internal pallidal segment (GPe, GPi) in two awake Rhesus monkeys before and after they were rendered hemiparkinsonian by unilateral intracarotid infusion of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Bursts were detected by the "surprise" method. In the normal state, interspike intervals (ISIs) preceding or following bursts were frequently significantly longer than the average baseline ISI, and their duration was correlated with the burst length (i.e., the number of spikes/burst). Significant correlations were also found in all three structures between the burst length and the duration of interburst intervals. The incidence of burst discharges and the proportion of time spent in bursts increased in GPe, STN, and GPi after MPTP treatment. Burst lengths became more tightly related to preburst ISIs in the STN after MPTP treatment and to postburst ISI duration in all three structures. These results show that bursts in spontaneous GPe, STN, and GPi discharge are often preceded or followed by long ISIs, and that burst length, the length of pre- and postburst ISIs, and the length of interburst intervals are related to one another. Complex changes in these interactions may contribute to abnormal information processing in parkinsonism.