Role of basal ganglia in behavioral learning.

Recent studies on single neuron activity revealed that activities of many basal ganglia neurons are dependent upon the behavioral context. This may give us a reason why observed movement-related activity in the basal ganglia occurred late in relation to prime mover muscle activity. Early onset activity of primate putamen neurons was reported in a study in which animals were required to make a performance of sequential limb movements. This suggests the participation of basal ganglia in the initiation of movement in a behavioral context-dependent manner. The context-dependent activity in the basal ganglia has been shown to be acquired through learning. For instance, midbrain dopamine neurons respond to external sensory stimuli or reward only during early stages of learning motor tasks. Striate neurons acquire task-related activity through learning and the acquired activity almost disappears after selective lesions of nigrostriatal dopamine. In this article, a hypothetical scheme of basal ganglia functioning in behavioral learning is presented. Limbic input conveys information related to 'reinforcement' or 'incentive' either directly to the striatum or indirectly through nigrostriatal dopamine system, and it contributes to the acquisition and expression of learned activity in the striatum. The expression of learned striatal activity would contribute to the initiation of learned motor behavior.