Hypotheses for Hair Cell Ribbon Synapses Probed by a Biomimetic System

Abstract

The conversion of sound waves to electrical impulse in the auditory nerve of the inner ear takes place in the organ of Corti through the process of synaptic transmission in and around the ribbon synapse. Finding the relation between the functional and physiological characteristics of the ribbon synapse is one of the central issues in auditory science nowadays. There has been a hypothesis on inner hair cells (IHC) that complex broad band sounds can be encoded by multiple ribbon synapses in an IHC. We provide a hypothesis on the spectral analysis by multiple ribbon synapses, where heterogenous glutamate release rates in a IHC is the key to the spectral analysis. To demonstrate our hypothesis, we fabricate a neuromorphic device that models the hair cell bundle and its afferent neuron, and investigate its response to pure-tone and human voice sounds. Our biomimetic experimental results go beyond theoretical simulation While mechanical oscillators’ velocity dependence of relaxation and noise can not but be assumed theoretically, our biomimetic approach goes beyond this limitation of such assumption and is self-consistent by its own. We observe that for the neuronal spike rates to mimic the voice sound signal of a word, a distribution of the spontaneous neurotransmitter relaxation rates is necessary. We also discuss a physical microscopic model for the ribbon synapse which is based on charge transport theory.