The substantia nigra is a small brain region located in the tegmentum of the mesencephalon. It comprises two major sub-regions, the pars compacta (SNc), made up of dopaminergic neurons and the pars reticulata that comprises GABAergic cells similar to those of the globus pallidus interna. It is involved in the regulation of important brain functions including motor, reward-related and cognitive behaviors. Abnormal functioning or degeneration of neurons in the substantia nigra pars compacta is associated with Parkinson's disease, drug addiction, epilepsy and various psychiatric disorders.
Smith, Y., & Masilamoni, J. G. (2017). The Substantia Nigra ☆. In Reference Module in Neuroscience and Biobehavioral Psychology. Elsevier. https://doi.org/10.1016/b978-0-12-809324-5.00825-7