Chapter 25 - The Subthalamic Nucleus in Impulsivity

Abstract

Motor control is the result of a perfect balance between activation and inhibition of movement patterns. The basal ganglia are connected to the motor cortex, including a direct pathway that facilitates the preparation of movement patterns and an indirect pathway suppressing movement preparation. Anatomically and functionally the subthalamic nucleus (STN) holds a central position within the indirect pathway, acting like a brake on the motor system. Using a hyperdirect pathway—a monosynaptic connection between the key nodes of the inhibitory network—the presupplementary motor area and the inferior frontal gyrus are connected to the STN. Within the process of decision-making, the inhibitory network employs the STN function to pause the motor system. This has been specifically shown in decision conflicts, i.e., whenever an automatic response must be suppressed to have more time to choose between alternative responses. The cortical inhibitory network and the STN dynamically regulate the decision threshold as a function of decision conflict. In this way cognitive processes of active inhibition influence the motor system via the STN to regulate behavior.