Any of four masses of gray matter deep in the cerebral hemispheres below the cortex: the caudate, putamen, and the internal and external segments of the globus pallidus. The caudate and putamen form the corpus striatum; the putamen and globus pallidus form the lenticular nuclei. Parkinsonism and Huntington chorea are diseases of the basal nuclei, which are key components in the formation of habits and unconscious motor programs. The basal nuclei contribute to some of the subconscious aspects of voluntary movement (such as accessory and tremor-inhibiting movements). They do not initiate movement but provide coordination of complex motor circuits. Neurotransmitters that affect the basal nuclei are acetylcholine, dopamine, gamma-aminobutyric acid (GABA), and serotonin.

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