Segregation and convergence of information flow through the cortico-subthalamic pathways

Cortico-basal ganglia circuits are organized in parallel channels. Informat ion flow from functionally distinct cortical areas remains segregated withi n the striatum and through its direct projections to basal ganglia output s tructures. Whether such a segregation is maintained in trans-subthalamic ci rcuits is still questioned. The effects of electrical stimulation of prefro ntal, motor, and auditory cortex were analyzed in the subthalamic nucleus a s well as in the striatum of anesthetized rats. In the striatum, cells (n = 300) presenting an excitatory response to stimulation of these cortical ar eas were located in distinct striatal territories, and none of the cells re sponded to two cortical stimulation sites. In the subthalamic nucleus, both prefrontal and motor cortex stimulations induced early and late excitatory responses as a result of activation of the direct cortico-subthalamic path way and of the indirect cortico-striato-pallido-subthalamic pathway, respec tively. Stimulation of the auditory cortex, which does not send direct proj ection to the subthalamic nucleus, induced only late excitatory responses. Among the subthalamic responding cells (n = 441), a few received both prefr ontal and motor cortex (n = 19) or prefrontal and auditory cortex (n = 10) excitatory inputs, whereas a larger number of cells were activated from bot h motor and auditory cortices (n = 48). The data indicate that the segregat ion of cortical information flow originating from prefrontal, motor, and au ditory cortices that occurred in the striatum is only partly maintained in the subthalamic nucleus. It can be proposed that the existence of specific patterns of convergence of information flow from these functionally distinc t cortical areas in the subthalamic nucleus allows interactions between par allel channels.