Responses of cat pallidal neurons to cortical and subcortical stimuli

Abstract

Discharge patterns of pallidal neurons of the cat were studied during single-shock and sustained high-frequency stimulation of sensorimotor cortex (SMC), caudate nucleus, nonspecific thalamic nuclei (CM), subthalamus, midbrain reticular formation (MRF) and amygdaloid complex. Three types of spontaneous discharge pattern were found in pallidal neurons: high discharge rate (HDR), low discharge rate (LDR) and repetitive burst patterns were observed. The LDR and repetitively discharging units generally responded to a limited number of the stimulus sites, occasionally to one site exclusively, whereas HDR units generally showed a high degree of convergence. The response patterns of units responding to single-shock stimulation of MRF, CM, and subthalamus were similar. A marked facilitation lasting 20–50 msec was a consistent response which in some units was followed by a prolonged facilitation or inhibition. Sustained high-frequency stimulation always resulted in a net facilitatory effect. Single-shock stimulation of caudate nucleus and SMC generally produced a powerful inhibition. In some units facilitation preceded this inhibition, and in a small number of units, only facilitation was observed. Sustained high-frequency stimulation produced either inhibitory or facilitatory effects. Single-shock stimulation applied to amygdala caused an initial facilitation, followed in some units by inhibition or facilitation. High-frequency stimulation produced either facilitatory or inhibitory effects. The variation in response patterns to stimulation of each stimulus site was dependent upon the individual neuron and not upon the stimulus site. Analyses of the responses to a test stimulus following a conditioning stimulus suggest that the excitability changes of the neuron following single-shock stimulation are well represented by the poststimulus time histogram.