Modelling electrocochlear responses

Abstract

The cochlea is a central part of the inner ear handling the task of transforming acoustical waves into electrical impulses that are then carried by the sensory nerves further into the brain. Despite being one of the smallest organs in the human body its functionality is highly complex and even after long years of research a lot of its mechanics is not well understood. The current knowledge of the electro-mechanical functionality of the cochlea is mostly based on crude 2-dimensional model approximations and, while the clinical manifestation of certain mechanisms have been a subject of numerous scientific publications, the exact link between those two remains largely unexplored. Auditory potentials have elements thought to include components due to the receptor potentials of both inner- and outer hair cells. However, there is a deficiency of experimental and analytical research of these components and in particular their non-linear properties. If a reliable model that is able to simulate these components is produced, it may provide a tool for exploring how different pathologies are expected to show up in measurements of the cochlear microphonic and the new insight may lead to improved stimulus paradigms for extracting information about processes taking place in the cochlea. In this doctoral thesis, the current state of the cochlear modelling field is discussed and explored further to understand the non-linear processes taking place within the cochlea using numerical models with a focus on the auditory evoked potential – cochlear microphonic. A novel protocol for two-tone suppression in cochlear microphonic measurements in normal-hearing patients is also introduced in an effort to correlate the model predictions with the experimental data. The comparative analysis of the collected data set with the cochlear model simulation revealed that even though the model can successfully replicate in vivo measurements collected at a single point along the cochlea, at its present formulation, it cannot be used to reliably predict the cochlear microphonic recorded at the round window. This conclusion comes after the analysis of the experimental data indicated that the cochlear microphonic recorded by an extratymphanic electrode contains contributions from multiple locations along the cochlea, and not just from its basal segment, as it has been suggested in the past.

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Identifiers

ORCID for Ben Lineton: orcid.org/0000-0003-4784-7762

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