%0 Journal Article
%T How Basal Ganglia Outputs Generate Behavior
%A Henry H. Yin
%J Advances in Neuroscience
%D 2014
%R 10.1155/2014/768313
%X The basal ganglia (BG) are a collection of subcortical nuclei critical for voluntary behavior. According to the standard model, the output projections from the BG tonically inhibit downstream motor centers and prevent behavior. A pause in the BG output opens the gate for behavior, allowing the initiation of actions. Hypokinetic neurological symptoms, such as inability to initiate actions in ParkinsonĄ¯s disease, are explained by excessively high firing rates of the BG output neurons. This model, widely taught in textbooks, is contradicted by recent electrophysiological results, which are reviewed here. In addition, I also introduce a new model, based on the insight that behavior is a product of closed loop negative feedback control using internal reference signals rather than sensorimotor transformations. The nervous system is shown to be a functional hierarchy comprising independent controllers occupying different levels, each level controlling specific variables derived from its perceptual inputs. The BG represent the level of transition control in this hierarchy, sending reference signals specifying the succession of body orientations and configurations. This new model not only explains the major symptoms in movement disorders but also generates a number of testable predictions. 1. Introduction The basal ganglia (BG) have been implicated in functions as diverse as movement, learning, and motivation [1¨C5]. Damage to these nuclei impair or even abolish voluntary behavior. But after decades of research it remains unclear how the BG generate behavior. I shall argue that the BG occupy a specific level in a functional hierarchy. Unlike traditional models, which are based on the linear causation paradigm [6], the proposed hierarchy is based on the principle of cascade control [7]. Unfortunately control theory is currently misunderstood in neuroscience, mainly due to conceptual confusions introduced by cybernetics and engineering control theory. To understand the role of the BG in behavior, it would be necessary to explain the principles of control and the organization of the functional hierarchy. I shall first discuss current models of the BG and recent results that begin to challenge these models. I shall then explain how control theory, correctly applied, can help us understand behavior, and how different control systems can be arranged in a hierarchy using the principle of cascade control. Finally, I shall discuss the neural implementation of cascade control and the distinct contributions of the BG in this functional hierarchy. 2. What Are the Basal
%U http://www.hindawi.com/journals/aneu/2014/768313/