An Improved Model for the Rate–Level Functions of Auditory-Nerve Fibers
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Date
2011-10-26
Journal Title
Journal ISSN
Volume Title
Publisher
Society for Neuroscience
Abstract
Acoustic information is conveyed to the brain by the spike patterns in auditory-nerve fibers (ANFs). In mammals, each ANF is excited via
a single ribbon synapse in a single inner hair cell (IHC), and the spike patterns therefore also provide valuable information about those
intriguing synapses. Herewereexamine and model a key property of ANFs, the dependence of their spike rates on the sound pressure level
of acoustic stimuli (rate–level functions). We build upon the seminal model of Sachs and Abbas (1974), which provides good fits to
experimental data but has limited utility for defining physiological mechanisms. We present an improved, physiologically plausible
model according to which the spike rate follows a Hill equation and spontaneous activity and its experimentally observed tight correlation
with ANF sensitivity are emergent properties. We apply it to 156 cat ANF rate–level functions using frequencies where the mechanics are
linear and find that a single Hill coefficient of 3 can account for the population of functions. We also demonstrate a tight correspondence
between ANF rate–level functions and the Ca2 dependence of exocytosis from IHCs, and derive estimates of the effective intracellular
Ca2 concentrations at the individual active zones of IHCs.Weargue that the Hill coefficient might reflect the intrinsic, biochemical Ca2
cooperativity of the Ca2 sensor involved in exocytosis from the IHC. The model also links ANF properties with properties of psychophysical
absolute thresholds.
Description
Keywords
Auditory, Synapse, Spike Rate, Calcium, Hill Coefficient