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 su- perimposed. The similar shapes of the L-A functions at different frequencies may reflect the physical laws of sound being trans- ferred into bioelectric signals. The position of a non-CF L-A function could be measured as the differences of the asymptotic L and A （△L and △A） compared to the L-A function at a reference frequency such as the CF. The nerve fibers and synapses connect- ing 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 trans- duction, respectively. Thus, △L and △A may be measurements of the total length of nerve fibers and the strength of summated synapses in the activated auditory pathway. △L and △A differed between frequency channels and neurons, suggesting that the dif- ferences of acoustic neuronal responses are always caused by activation of different pathways, and that the pathways that process sounds are diverse.