This project addresses the question of how synaptic inputs from the striatum and subthalamic nucleus control the spiking output of globus pallidus neurons. Multiple subpopulations of GABAergic neurons coexist n the GP, and evidence indicates that the electrophysiological properties and modes of synaptic integration differ across GP neuron subtypes. To understand how synaptic inputs control spiking in different GP neurons, a combination of electrophysiological, histological and computational approaches will be used to address the ollowing two specific aims. Aim 1: to characterize the responses of GP neuron subtypes to excitatory and nhibitory synaptic inputs. Synaptic responses are characterized electrophysiologically. Neurons are post- processed immuhistochemically to determine which subpopulation they belong to. Aim 2: to determine how differing intrinsic properties influence synaptic integration in GP neuronal subpopulations. The intrinsic properties of each subtype will be characterized in detail. For both aims, biophysically realistic computer models are constantly refined according to the physiology data and used to make predictions about how the different neuronal subpopulations are likely to respond to complex, in vivo-like patterns of synaptic input.