Cochlear HEALTH
 
Speech preprocessing in CIsSpeech_processing_in_CI.htmlshapeimage_3_link_0
Additional information:
Cochlear anatomy in CIsCochlea.htmlshapeimage_5_link_0
Laser light stimulation studiesLaser_prosthesis.htmlshapeimage_6_link_0
Overview of existing neuroprosthesesNeuroprostheses.htmlshapeimage_7_link_0

Confocal microscopy reconstruction of cochlear microlesions induced by a microelectrode in a guinea pig. Two types of lesions were aimed at: lesions in primary afferents and lesions in the spiral ganglion. Using confocal microscopy it is possible to quantify the volume and the position of the lesion at high precision. Figure from Konerding et al. (2020).

The focus of our research project “Hearing Holes” is to understand the consequence of lesions in the cochlea on responsiveness to cochlear implant. The initial study by Shannon et al. (2002) documented the detrimental consequence of gaps in spectral information (caused by inactivating one or more electrodes of the cochlear implant) for speech understanding. Using tripolar stimulation (Kral et al., 1998), our cooperation partner Prof. J. Arenberg (Harvard Medical School) documented variable electrical stimulation thresholds along the auditory nerve in human subjects (Arenberg, 2010). This is likely the consequence of a variable survival of spiral ganglion cells. “Cochlear health” describes the condition of the spiral ganglion and organ of Corti relevant for cochlear implantation.
To provide the evidence base and to better understand the consequence of such variations, we initiated a study the consequences of small lesions in animal experiments, where a lesion can be induced and objectively (independently) controlled by histology. Combining µCT and confocal microscopy imaging with state-of-the-art multielectrode recordings thus allows quantifying and assessing both the lesion size and its central neuronal consequence. 
In a pilot study we could document that there are local and global cochlear effects of lesions with size of up to 400 µm diameter (Konerding et al., 2022). Anatomic and functional lesion size were highly correlated, however, as expected, the functional lesions were significantly larger than the anatomic lesions. Furthermore, using compound action potentials evoked by cochlear implant we could identify a correlate of cochlear lesions: they differentially affected cathodic leading and anodic leading biphasic pulses.
As a consequence, we focus on polarity effects in ongoing studies. Cochlear_Health_files/HearRes98.pdfshapeimage_8_link_0

Using a combination of confocal microscopy (with high special resolution) and µCT it is possible to relate the position of the cochlear implant (blue) to the microlesion in the cochlea (red). Using this approach we can identify which contacts are how close to the individual implant electrodes.

Figure from Konerding et al. (2022).

CI as a teragnostic probeTeragnostic_probe.htmlshapeimage_9_link_0

Methodology of the investigation of the impact of cochlear lesions on the representation of cochlear implant stimulus. Small lesions are placed by a microelectrode either in the dendrites or the cell bodies of spiral ganglion cells. Left: Drawing of the experimental setup. Right: Photograph from the experiment with cochleostomy (coch) and a small lesion in the modiolus (arrow). The round window (rw) is covered by the ball electrode (be) for compound action potential recordings.

Figure from Konerding et al. (2022).