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T. Potrusil, C. Wenger, R. Glückert, A. Schrott-Fischer, F. Rattay:
"Morphometrical differences of human spiral ganglion cells: what does it mean for electrical stimulation?";
Talk: 48th Inner Ear Biology Workshop, Lisabon; 2011-09-18 - 2011-09-21.

Objective: The sizes of unmyelinated spiral ganglion cells (SGC) in the human cochlea have a powerful impact on the action potential (AP) travelling from the hair cell to the auditory cortex. The aim of the study was to analyze these spike-barriers morphometrically and mimic different stimulation strategies. Furthermore, new information about the distribution of SGC in the different regions of the inner ear was
acquired and their impact concerning electrical stimulation was studied.
Methods: Two human cryoembedded cochleae from different subjects have been serially sectioned perpendicular and radial respectively to the modiolus with a section thickness of 35 μm providing to have bipolar SGC in their full dimensions on each cryosection. Immunohistochemistry including confocal microscopy has been performed
for detecting perikarya and their appropriate nuclei. These structures were segmented manually for calculating the volumes. For determining different cell populations hierarchical cluster analysis was performed. A compartment model of the human cochlea neuron was used to determine intra- and extracellular excitation thresholds, the
point of spike generation and the action potential delay over the soma.
Results: Hierarchical clustering of perikarya volumes revealed four distinct populations of SGC within the human cochlea. The somatic volume (n=146) varies enormously between 532 and 8258 μm³ resulting in delay differences of the generated AP passing the soma in extracellular stimulation. The excitation thresholds for an AP passing a soma are ranging from -171 μA to -480 μA respectively using monophasic stimulation.
Conclusion: Systematic morphometric measurements on two human inner ears indicate four different sub-populations of spiral ganglion cells. In extracellular stimulation the variation in perikarya size results in different excitation thresholds as well as different
points of spike initiation. These resulting spike delays over the unmyelinated cell soma lead to variations of the temporal pattern which might be an important component for speech understanding.