An approach to identify the functional transduction and transmission of an activated pathway

In this study, we investigated the features of latency-amplitude ( L-A ) functions at different sound frequencies, using extracellular recording from auditory neurons in the central nucleus of the inferior colliculus (ICC) in mice. Isofrequency L-A functions from single neurons could be fit with a newly developed equation based on Pieron’s law. The high degree of fitness indicates that the curvatures of all isofrequency L-A functions for a given neuron are similar, and that the difference between L-A functions is due to a shift in their positions in the coordinate system. When we normalized the L-A functions to match the position of the L-A function obtained at the neuronal characteristic frequency (CF), all isofrequency L-A functions from a given ICC neuron were highly superimposed. The similar shapes of the L-A functions at different frequencies may reflect the physical laws of sound being transferred into bioelectric signals. The position of a non-CF L-A function could be measured as the differences of the asymptotic L and A ( ΔL and ΔA ) compared to the L-A function at a reference frequency such as the CF. The nerve fibers and synapses connecting to a neuron for acoustic information processing can be functionally simplified as a single “wire” (as the total length of nerve fibers) and “joint” (as the summated size/strength of synapses). The wire and joint mediate information transmission and transduction, respectively. Thus, ΔL and ΔA may be measurements of the total length of nerve fibers and the strength of summated synapses in the activated auditory pathway. ΔL and ΔA differed between frequency channels and neurons, suggesting that the differences of acoustic neuronal responses are always caused by activation of different pathways, and that the pathways that process sounds are diverse.