As an anatomist he was one of the first to use coronal sections of the brain and to use alcohol to aid dissection. He described the locus coeruleus, the locus niger (substantia nigra) in the brain, in 1786, and the band of Vicq d'Azyr, a fiber system between the external granular layer and the external pyramidal layer of the cerebral cortex, as well as the Mamillo-thalamic tract, which bears his name. His systematic studies of the cerebral convolutions became a classic and Vicq d'Azyr was one of the first neuroanatomists to name the gyri. He studied the deep gray nuclei of the cerebrum and the basal ganglia. He participated in the Second Encyclopedia.