Basal ganglia: functional anatomy and physiology. Part 2

Advances in knowledge about basal ganglia function and circuitry are reviewed. Despite the voluminous available literature on this subject, the role of basal ganglia in health and disease remains controversial. Experimental data on the effects of stimulation and ablation of the basal ganglia are summarized. The roles of the basal ganglia in the preparation for and execution of cortically initiated movement are described. Newer roles ascribed to the basal ganglia in sensory-motor gating, cognition, emotion, and motivation are discussed. The old and current concepts of information flow between the cerebral cortex, striatum, pallidum, thalamus, and back to the cerebral cortex are reviewed. The "funnel" system of information flow has been discarded in favor of several parallel and largely segregated loops pertaining to motor, oculomotor, cognitive, and limbic functions. The anatomic substrate of each of these loops is described. The specific roles of the striatum, pallidum, substantia nigra, and thalamus in information flow as related to movement are described. The roles of the basal ganglia in reinforcing wanted behavior and suppressing unwanted behavior via direct and indirect striatal loops are discussed. The implications of these loops in the genesis of Parkinson's disease and Huntington's chorea are described. Alteration in basal ganglia neurotransmitters and neuromodulators in Huntington's chorea, Tourette's syndrome, and Parkinson's disease are described.