Spiral-ganglion survival and regenerative interfaces

The CI stimulates spiral ganglion neurons (SGNs), the primary auditory afferents; their number, health, and peripheral-process integrity vary widely across deaf etiologies and decline over the years of deafness. Because current spread is broad, performance is thought to depend less on raw SGN count than on having a spatially patchy-but-sufficient population close to the array — but the relationship is loose, and no in-vivo method yet counts living SGNs in a patient, which is a major gap in individualizing therapy.

The regenerative frontier aims to bring neurons and electrodes closer, or to protect and restore the nerve: neurotrophin (BDNF, NT-3) delivery — via drug-eluting arrays, coated electrodes, or cell/gene therapy — can, in animals, induce SGN peripheral neurite resprouting toward the electrode, lowering thresholds and potentially sharpening spatial tuning. Combined with efforts at hair-cell regeneration and inner-ear gene therapy for specific genetic deafness, these blur the line between a prosthesis and a biological repair, but human evidence remains early and the durability and safety of chronic neurotrophic stimulation are unproven.