Input‐Output Characteristics of the Lateral‐Line Organ of Xenopus laevis

In Xenopus laevis, the lateral‐line system may be considered as a single organ, containing about 20 000 hair cells, that is used to detect moving objects. From anatomical and neurophysiological evidence, it appears to be organized in groups of sensory buds, called stitches, which are directionally sensitive, probably to velocity. Each stitch is innervated by two large myelinated afferent fibers and by a few small myelinated and unmyelinated fibers, which may be efferent. Electrophysiological recordings made from a piece of skin in vitro show that the two large fibers are spontaneously active and sensitive to motion in opposite directions. The spontaneous activity in each fiber is independent of spontaneous activity in the other, indicating that the origin of spontaneous activity cannot be Brownian motion of the cupula. Interval histograms of spontaneous activity show an exponential tail for long intervals and a decrease in the number of 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 intensity. These results indicate that both place and pulse‐position coding is used to convey the information necessary for the perception proper to this organ.