The Functional Organization of the Auditory Brainstem in the Mustache Bat and Mechanisms for Sound Localization

Abstract

The ability of bats to orient and successfully avoid obstacles in total darkness has been of interest to scientists for more than two centuries. Although audition has always been strongly associated with this ability, general acceptance of orientation by sound came only around 1940 with the elegant studies of Griffin and his colleagues (Griffin and Galambos 1941; Galambos and Griffin 1942; an excellent summary of this work is provided in Griffin 1958). They showed that bats are not only able to navigate through complex environments but they also can detect, identify and locate prey in the night sky by emitting loud ultrasonic calls and listening to the echoes that are reflected from nearby insects. Griffin (1944) coined the term echolocation to describe this form of biological sonar. However, it was not until the early 1960s that Alan Grinnell (Grinnell 1963 a,b,c,d) and Nobuo Suga (1964a, b) published the first reports of neural processing of ultrasonic signals by echolocating bats. A few years later, in 1967, Grinnell (1967) reported that the evoked potentials from the inferior colliculus of the mustache bat, a species that had not previously been studied, differed from comparable neural potentials seen in any other animal. The unique feature was that the thresholds of the neural potentials were very sharply tuned to about 60 kHz, the dominant frequency of the mustache bat’s orientation calls.