Any of four deeply placed masses of gray matter (as the amygdala) in each cerebral hemisphere. Location: The basal ganglion is located deep within the cerebral hemispheres in the telencephalon region of the brain. It consists of the corpus stratium, subthalamic nucleus and the substantia nigra.

Subcortical masses of gray matter in the forebrain and midbrain that are richly interconnected and so viewed as a functional system. The nuclei usually included are the caudate nucleus (caudoputamen in rodents), putamen, globus pallidus, substantia nigra (pars compacta and pars reticulata) and the subthalamic nucleus. Some also include the nucleus accumbens and ventral pallidum.