The brain of an echo locating bat is devoted, in large part, to analyzing sound and conducting behavior in a world of sounds and echoes. This monograph is about analysis of sound in the brainstem of echolocating bats and concerns the relationship between brain structure and brain function. Echolocating bats are unique subjects for the study of such relationships. Like man, echolocating bats emit sounds just for the purpose of listening to them. Simply by observing the bat's echolocation sounds, we know what the bat listens to in nature. We therefore have a good idea what the bat's auditory brain is designed to do. But this alone does not make the bat unique. The brain of the bat is, by mammalian standards, rather primitive. The unique aspect is the combination of primitive characteristics and complex auditory processing. Within this small brain the auditory structures are hypertrophied and have an elegance of organization not seen in other mammals. It is as if the auditory pathways had evolved while the rest of the brain remained evolutionary quiescent.

nerve; subsequently, however, they concluded that the recordings had been from aberrant cells of the cochlear nucleus lying central to the glial margin of the VIII nerve (GALAMBOS and DAVIS, 1948). The first successful recordmgs from fibres of the cochlear nerve were made by TASAKI (1954) in the guinea pig. These classical but necessarily limited results were greatly extended by ROSE, GALAMBOS, and HUGHES (1959) in the cat cochlear nucleus and by KATSUKI and co-workers (KATSUKI et at. , 1958, 1961, 1962) in the cat and monkey cochlear nerve. Perhaps the most significant developments have been the introduction of techniques for precise control of the acoustic stimulus and the quantitative analysis of neuronal response patterns, notably by the laboratories of KIANG (e. g. GERSTEIN and KIANG, 1960; KIANG et at. , 1962b, 1965a, 1967) and ROSE (e. g. ROSE et at. , 1967; HIND et at. , 1967). These developments have made possible a large number of quanti tative investigations of the behaviour of representative numbers of neurons at these levels of the peripheral auditory system under a wide variety of stimulus conditions. Most of the findings discussed herein have been obtained on anaesthetized cats. Where comparative data are available, substantially similar results have been obtained in other mammalian species (e. g. guinea pig, monkey, rat). Certain significant differences have been noted in lizards, frogs and fish as would be expect ed from the different morphologies of their organs of hearing (e. g.