Changing concepts of nigral dopamine system function within the basal ganglia: relevance to extrapyramidal disorders

The recent discovery of new methods for tracing brain pathways and studying their function has greatly expanded our knowledge of the areas of the brain involved in extrapyramidal disorders and has begun to change our concept of how these areas function. One such change has involved our understanding of the role of the dopaminergic system within the basal ganglia. Rather than dopamine being seen primarily as a major influence on striatal output it is now perhaps best conceptualized as one link in a set of circular pathways, one of whose functions is to modulate nondopaminergic output from the substantia nigra to other brain regions. In addition, new evidence suggests that this neurotransmitter system may play a role in the way sensory inputs are handled by the basal ganglia. These new roles for the nigral dopaminergic system raise important new questions about its function in extrapyramidal motor systems as well as provide possible answers to questions concerning the mechanisms underlying some of the symptoms seen in disorders involving the basal ganglia.