Tuning curves of auditory nerve fibers in the alligator lizard

Abstract

Action potentials were recorded from single units in the auditory nerve with electrodes placed between the ganglion cell bodies and the habenula perforata. Tuning curves of units fell into two distinct populations: a low-frequency group with characteristic frequencies (CF) below 1 kHz, and a high-frequency group with CF above 1 kHz. Units with low CF were located in the part of the nerve that enters the optical region of the basilar papilla, while units with high CF were located in the part of the nerve that enters the basal region of the basilar papilla. Tuning curves from these two regions have markedly different shapes. The sensory epithelium in these two regions differs in presence of the tectorial membrane, orientation of the hair cells, and length of the ciliary tufts. These results suggest that tuning properties of auditory nerve fibers in this animal may not be entirely due to the frequency selectivity of the basilar membrane. [Supported by NIH grants.]