Subdivisions of the inferior colliculus in the barn owl (Tyto alba).

The inferior colliculus in the barn owl contains three subdivisions: the central (ICC), external (ICX), and superficial (ICS) nuclei. The nuclei are distinguished on the basis of their cyto- and myeloarchitecture, connectivity, and physiological properties. The ICC may be further divided into dorsal (ICCd) and ventral (ICCv) parts. Auditory fibers ascending in the lateral lemniscus enter the ICCd and ICCv, but not the ICX or ICS. The ICX receives its auditory input from the ICC. The ICC and ICX in owls are similar in position, anatomy, connectivity, and physiology to the ICC and ICX in mammals, suggesting that these structures are homologous. Units in the ICC are organized tonotopically, whereas units in the ICX are organized according to the locations of their spatial receptive fields. This implies that a transformation from a tonotopic to a spatiotopic organization takes place in the ICX of the owl.