Basal Ganglia Functionality

In discussing the precise functionality of the basal ganglia (which is still very much a matter for debate), it is worthwhile to introduce the idea of a motor plan. A motor plan ``represents an action requiring the sequential operation of simple motor acts (or motor programs)'' [6]. It seems to be generally agreed that the basal ganglia have something to do with the creation and/or execution of motor plans.

Kandel et al. [32] propose that the basal ganglia

• facilitate some motions, and suppress others, or
• compare motor commands with feedback from the evolving motion, or
• are involved with the initiation of internally generated movements.

As they point out, the third possibility is consistent with the difficulty persons with Parkinson's disease have in initiating motion.

Similarly, a recent paper by Kimura et al. [35] mentions three models for basal ganglia function in the literature.

• Denny-Brown and Yanagisawa's model [13], which posits that the basal ganglia are a ``clearing-house'', facilitating some cortical input while suppressing the rest.

• Marsden's model [42], that the basal ganglia handle automatic execution of learned motor programs.

• Miller and DeLong's model [49], that the basal ganglia have a motor command monitoring function.

Steg and Johnels [73] suggest that the basal ganglia are a sort of ``auto-pilot'':

the basal ganglia may be regarded as the autopilot controlling on a subconscious level the coordination in a distributed computer system built up by different motor programs, and by this activity gives the environmentally well-informed pilot, the cortex, optimal conditions for integrating information and selecting the target for direct, precise, and well-prepared actions undisturbed by a multitude of internal control functions.