The basal ganglia: from motor commands to the control of vigor
Vertebrates are remarkable for their ability to select and execute purposive actions: motor skills that are critical for thriving in complex, competitive environments. Over the past several decades there has been substantial progress in understanding how the central nervous system controls the execution of both stereotyped movements and selects purposive actions defined by their outcome. However, a number of fundamental questions remain. Motor skills are also actions that can be reliably performed despite substantial variation in kinematics and varied initial conditions. This raises the question of what circuits are responsible for the flexible parameterization of movement and how the goals of action are represented. In this piece we focus on one issue in particular: the role of subcortical circuits, specifically the basal ganglia, in the control of motor skills. We propose that the basal ganglia evolved from a circuit responsible for the command of simple movements to a more circumscribed role in implicit motivation – the control of ‘vigor’: the speed, frequency and amplitude of movements.