Lesion of the subthalamic nucleus or globus pallidus does not cause chaotic firing patterns in basal ganglia neurons in rats.

The basal ganglia appears to play an important role in behavioral selection. One model (Berns and Sejnowski's) of basal ganglia function argues that the subthalamic nucleus plays a critical role in this selection process and predicts that the subthalamic nucleus prevents the basal ganglia and its re-entrant circuits with the thalamus and cerebral cortex from developing chaotic oscillations. We tested this prediction by generating three-dimensional sequential interval state space plots of the spike trains from 684 globus pallidus, substantia nigra pars reticulata and subthalamic neurons recorded in intact, subthalamic lesioned and globus pallidus lesioned rats, neurons which had previously been analyzed with more standard statistical methods. Only 1 neuron (a globus pallidus neuron in a subthalamic lesioned rat) of the 684 showed a chaotic attractor. In no case did subthalamic nucleus lesion induce a chaotic firing pattern elsewhere in the basal ganglia.