Input-Output Characteristics of the Lateral-Line Sense Organs of <i>Xenopus laevis</i>

Abstract

In the toad Xenopus laevis, the lateral line system may be considered as a single organ, containing about 30 000 hair cells, which is used to detect moving objects. It is organized in groups of neuromasts, called stitches, which are directionally sensitive to water velocity. Each stitch is innervated by two large (∼8 μ) myelinated fibers. Electrophysiological recordings made from the nerve to a piece of skin in vitro show that these two fibers are spontaneously active and are sensitive to water velocities in opposite directions. The spontaneous activity in one fiber may have a slight positive correlation with the spontaneous activity in the other. This indicates that the origin of the spontaneous activity should not be Brownian motion of the cupula. Its origin is probably in the portion of the nerve between the hair cells and the start of myelination. Interval histograms of spontaneous activity show an exponential tail for long intervals and few small intervals. There is a characteristic absence of intervals less than about 10 msec. Evoked responses are repetitive, with rate, number of spikes, and latency, dependent on stimulus intensity. These results indicate that both place and pulse position coding could be used to convey the information necessary for the perception proper to this organ.