Spike generation in the lateral-line afferents ofXenopus laevis: Evidence favoring multiple sites of initiation

Abstract

1. Arrival-time differences of spikes recorded simultaneously at two sites from single lateral-line afferent fibers often fall into distinct populations, or have broad distributions. These findings are consistent with the notion that spikes arise at several different points within the branches of the afferent fibers. 2. Mechanical stimulation of an individual neuromast emphasizes one class of relative arrival-times, as would be expected if there were multiple sites of spike initiation. 3. During single-neuromast mechanical stimulation, spikes belonging to the emphasized classes are more tightly locked to the stimulus than are other spikes. This finding would also be anticipated under the hypothesis of multiple spike-initiation sites. 4. Coupling the evidence for multiple loci of spike generation with previously described indications of “resetting” after each spike, we propose that sensory messages transmitted fromXenopus lateral-line organs might be characterized by order statistics. This type of sensory process has not heretofore been studied. 5. The type of operation suggested for the lateral-line organs may be relevant to other acoustico-lateralis organs.