Sensory Processing in the Peripheral Auditory System of Treefrogs (<i>Hyla</i>)

Abstract

Responses to various sounds were recorded from single fibers in the auditory nerve of the green treefrog (Hyla cinerea) and the barking treefrog (H. gratiosa). Based on their sensitivity to tones, units fall into one of three distinct classes. In H. cinerea, one class is most sensitive to low frequencies 100–500 Hz; a second class is most sensitive to 500–1200 Hz; the third class responds best to 3100–3800 Hz. In both species, responses of low-frequency fibers can be inhibited by addition of energy in the corresponding mid-frequency range. This inhibition originates in the inner ear; it is not due to efferent activity. Responses of the other fibers cannot be inhibited. Most units in each class are spontaneously active. Thresholds within each class vary over a wide range; firing rates of individual fibers increase monotonically over an intensity range of about 40 dB. Fibers in each class can “follow” pulse repetition rates up to 250–400/sec. Our results suggest that the peripheral auditory system of treefrogs is well-suited to detect signals of species-specific significance. [Supported by NSF Grant GB-18836 and NIH Grant NS-09244.]