How do the lateral and medial segments of the globus pallidus differ?

The lateral and medial segments of the globus pallidus differ primarily in their connectivity and functional roles within the basal ganglia motor circuit.1

While both segments are cytologically similar and receive GABAergic terminals from the striatum, they are distinguished by the following:

• Input: The medial segment receives substance P fibers, whereas the lateral segment receives enkephalinergic projections.1
• Output and Function: The medial segment serves as a major output nucleus of the basal ganglia, projecting to the thalamus to influence motor function in the cerebral cortex. In contrast, the lateral segment projects almost exclusively to the subthalamic nucleus, from which it also receives reciprocal input.21