Central Auditory Pathways of Nonmammalian Vertebrates

The bulk of what is known about central auditory circuitry in vertebrates is chiefly derived from non-experimental descriptive anatomical studies most of which were made during the first thirty years of this century. It is a tribute to the skill and patience of the investigators of that time that much of their work has proved correct in the light of reinvestigation with modern methods of study and the increase in general knowledge of nervous system organization and function. With the introduction by Nauta and his co-workers in the 1950’s of experimental silver impregnation methods for the demonstration of degenerating axons and axon terminals, the opportunity to re-study these pathways with far greater accuracy and completeness became available. This is particularly true if electron microscopy, the Golgi methods, and the new autoradiographic tracing techniques are brought to bear in conjunction with the experimental silver methods. In spite of the opportunities presented, relatively few modern anatomical studies of the central auditory pathways of non-mammalian vertebrates have appeared; this contrasts sharply with the current interest in the central visual pathways. The best known non-mammalian auditory system is that of the pigeon, Columba livia (Boord and Rasmitssen, 1963; Karten, 1967, 1968; Boord, 1968).