Separation of Channels Subserving Approach and Avoidance/Escape at the Level of the Basal Ganglia and Related Brainstem Structures

Abstract

Abstract: The basal ganglia have the key function of directing our behavior in the context of events from our environment and/or our internal state. This function relies on afferents targeting the main in- put structures of the basal ganglia, entering bids for action selection at the level of the striatum or sig- nals for behavioral interruption at the level of the subthalamic nucleus, with behavioral reselection fa- cilitated by dopamine signaling. Numerous experiments have studied action selection in relation to in- puts from the cerebral cortex. However, less is known about the anatomical and functional link be- tween the basal ganglia and the brainstem. In this review, we describe how brainstem structures also project to the main input structures of the basal ganglia, namely the striatum, the subthalamic nucleus and midbrain dopaminergic neurons, in the context of approach and avoidance (including escape from threat), two fundamental, mutually exclusive behavioral choices in an animal’s repertoire in which the brainstem is strongly involved. We focus on three particularly well-described loci involved in ap- proach and avoidance, namely the superior colliculus, the parabrachial nucleus and the periaqueductal grey nucleus. We consider what is known about how these structures are related to the basal ganglia, focusing on their projections toward the striatum, dopaminergic neurons and subthalamic nucleus, and explore the functional consequences of those interactions.