A consideration of sensory factors involved in motor functions of the basal ganglia

There is a sizeable literature concerning basal ganglia (BG) functioning that is based on data from experiments employing a method of analysis that is traditionally used with other motor areas. A brief review of this literature is presented and the following conclusion is reached: as compared to the success of traditional methodologies in elucidating the workings of other motor systems, their use in BG investigations has proven disappointing. A possible reason for the shortcomings of traditional analyses in BG research is discussed. The remainder of this review concerns an alternative approach to the study of the BG that follows from consideration of a variety of clinical and experimental findings. The literature suggests that sensory aspects of BG functioning must be taken into account to fully appreciate the role of this system in motor control. A review of the literature concerning the latter suggests two points: The BG function as sensory analyzer for motor systems. That is, the BG convert sensory data from a form that is receptor oriented to a form that is relevant for guiding movement. The BG ultimately affect movement by gating sensory inputs into other motor areas rather than by directly affecting these areas. This sensory-based model of BG functioning explains a number of apparent discrepancies in the literature. In addition, seemingly anomalous findings are reconciled with the overwhelming evidence that the BG are a motor system. In particular, the suggestions of a BG role in attention and cognition are viewed as being intrinsic rather than orthogonal to the role of the BG in movement.