The basal ganglia have become a focus for work on neurotransmitter interactions in
the brain. These structures contain a remarkable diversity of neuroactive substances,
organized into functional subsystems that have unique developmental histories and
vulnerabilities in neurodegenerative diseases. A new view of the basal ganglia is
emerging on the basis of this neurochemical heterogeneity, suggesting that dynamic
regulation of transmitter expression may be a key to extrapyramidal function.