ABSTRACT
When the inner hair cells of the cochlea are destroyed, the neural activity conveyed
to the central auditory system is reduced. How does the central auditory system respond
when it is deprived of information? To address this question, inner hair cells in
the chinchilla cochlea were selectively destroyed with carboplatin. Inner hair cell
lesions had no effect on distortion product otoacoustic emissions or the cochlear
microphonic potential, showing that the outer hair cells were functionally intact.
Recordings from single auditory nerve fibers showed that the surviving inner hair
cells and type I neurons had normal thresholds and sharp tuning. The only notable
deficit was a reduction of the compound action potential from the auditory nerve in
proportion to the amount of inner hair cell loss. Despite reduced input from the cochlea
and auditory nerve, the local field potentials in the inferior colliculus and the
auditory cortex were not consistently reduced. In fact, potentials in the auditory
cortex were frequently larger than normal. Enhancement of the cortical potential may
be due to loss of γ-aminobutyric acid (GABA)-mediated inhibition. The data show that
when the inner hair cells of the cochlea are damaged, the central auditory system
increases its gain to compensate for a reduced sensory input.
KEYWORDS
Chinchilla - inner hair cells - auditory cortex - inferior colliculus - inhibition
- central auditory system
