Abstract
The human inner ear has an intricate spiral shape often compared to shells of mollusks, particularly to the nautilus shell. It has inspired many functional hearing theories. The reasons for this complex geometry remain unresolved. We digitized 138 human cochleae at microscopic resolution and observed an astonishing interindividual variability in the shape. A 3D analytical cochlear model was developed that fits the analyzed data with high precision. The cochlear geometry neither matched a proposed function, namely sound focusing similar to a whispering gallery, nor did it have the form of a nautilus. Instead, the innate cochlear blueprint and its actual ontogenetic variants were determined by spatial constraints and resulted from an efficient packing of the cochlear duct within the petrous bone. The analytical model predicts well the individual 3D cochlear geometry from few clinical measures and represents a clinical tool for an individualized approach to neurosensory restoration with cochlear implants.
Highlights
The human inner ear has an intricate spiral shape often compared to shells of mollusks, to the nautilus shell
Grouping the 108 cochleae into quartiles of the ratio of how the modiolus cuts the B-axis into Ba and Bb (Fig. 1c) reveals vertical trajectories that transform from ‘rollercoaster’ to ‘sloping’ (Fig. 2b)
‘Rollercoaster’ cochleae frequently include a vertical jump at the point where the second turn reaches the first turn
Summary
The human inner ear has an intricate spiral shape often compared to shells of mollusks, to the nautilus shell. It has inspired many functional hearing theories. The reasons for this complex geometry remain unresolved. A 3D analytical cochlear model was developed that fits the analyzed data with high precision. The cochlear geometry neither matched a proposed function, namely sound focusing similar to a whispering gallery, nor did it have the form of a nautilus. The analytical model predicts well the individual 3D cochlear geometry from few clinical measures and represents a clinical tool for an individualized approach to neurosensory restoration with cochlear implants
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