Julian R A Wooltorton, Ph.D.

The Research

University of Pennsylvania

Probing the inner hair cell bundle displacement-quantal synaptic response transfer function

How do submicron displacements of hair bundles on inner hair cells lead to a neural code perceived as sound? This proposal investigates the critical relationship (or transfer function) between hair bundle displacements and afferent fiber bouton responses in the gerbil cochlea. Understanding how we encode the acoustic wave into sound is vital to hearing research. By investigating the relationship between the response to acoustic waves of sensory cells in the cochlea and the resulting postsynaptic neuronal response, we will provide vital information on how the first synapse in the auditory pathway works. This is the basic step carried out by cochlear prostheses. Further insight into the biological details of this encoding step promise new insight into how to improve the design and performance of cochlear prostheses, and help to further ameliorate hearing loss and deafness. Mechanical energy of an acoustic wave enters the ear en route to the cochlea where it is translated into the electrical signals of the auditory nerve. This process involves numerous steps dependent upon the unique architecture of the mammalian ear and various specialized cellular processes to maintain fidelity in reporting frequency, amplitude, timing, and range of auditory stimuli. The inner hair cell processes acoustic waves in the cochlea. A hair bundle atop this cell senses acoustic stimulus and allows current to flow into the hair cell. This ultimately results in neurotransmitter release onto an afferent fiber bouton and subsequent sound perception. One of the true wonders of the biological world is the ability of the auditory system to detect the nearly molecular scale displacements of the hair bundle that result from acoustic wave stimulation. How these tiny displacements lead to a neural code that we perceive as sound is poorly understood. In this application, we propose to define the quantitative relationship (transfer function) between inner hair cell bundle displacement and the quantal response in the afferent fiber bouton.