Human cochlear nerve model

19.08.2009 - 18.08.2012
Research funding project
The main purpose of the project is to gather new detailed anatomic and morphometric information about the afferent part of the human cochlear nerve (spiral ganglion) and to use this data in a new computational model for analyzing input output relations for both the acoustically and the electrically stimulated ear. Moreover, the pathways of the spiral ganglion cells will be investigated. The results are of considerable interest to the cochlear implant research in order to overcome shortcomings like speech understanding in a noisy environment. The neural elements responsible for signal transport from the cochlea to the brain show essential anatomic differences between man and mammalian species, leading to several non tested and unproved hypotheses concerning functional consequences. Currently the signaling strategies for cochlea prostheses are mainly based on single fiber recordings in cat. Due to missing fundamental investigations on the neural elements of the human cochlea neurons, even the latest signal processing strategies for cochlear implant users are de facto designed for cats instead of humans. Most striking for the uniqueness of the human spiral ganglion cells is the soma region, typically with (i) poor insulation by myelin and (ii) clusters containing several cell bodies. A goal of the project is to expand to a large extent our knowledge about the relevant ultra-structure. Using existing equipment and material (temporal bones from several individuals and a selection of inner ears from primates) allows to quantify human peculiarities. A comparison with primates should give a clue about the development of the unique morphological features in humans. As an alternative to single fiber recordings which are not available for humans, we will develop a general biophysical model for cochlear neurons including cluster properties in order to understand the functional consequences of neuron variability seen in mammals and humans by analyzing the influence of relevant geometric and electric parameters. With this model we will analyze how the three main auditory nerve coding principles (i-iii) in man are related with the specific human anatomy and morphometry and, additionally, we will include a discussion about consequences for cochlear implants. In more detail, the model analysis is concerned with (i) tonotopic organization: a shift in frequency mapping concerning distal fiber endings originating in the organ of Corti (almost 2¿ cochlear turns) and soma regions in Rosenthal canal (1¿ turns), (ii) temporal fine structure of the neural code: a) for short interspike intervals in the distal axon there is a possible loss of signals when passing the soma region and b) in case of electrical stimulation: a confusing bimodal distribution of delay times as a consequence of more than one spike initiation regions along a single cochlear neuron (iii) spontaneous spiking is a supporting mechanism for acoustic signals just above the hearing threshold resulting in a mix of spikes with and without temporal information about the acoustic input; clusters of several somas may act as filter elements as a first step in neural code processing.

People

Project leader

Project personnel

Institute

Grant funds

  • FWF - Österr. Wissenschaftsfonds (National) Austrian Science Fund (FWF)

Research focus

  • Beyond TUW-research focus: 40%
  • Computational System Design: 10%
  • Modeling and Simulation: 50%

Keywords

GermanEnglish
Spiral ganglionspiral ganglion
Cochleacochlea
MorphometrieMorphometrie
Computersimulationcomputer simulation

External partner

  • Universitätsklinik für Hals-Nasen-Ohrenheilkunde Medizinische Universität Innsbruck

Publications