Centrifugal Signals from the
Central Nervous System to Lower Auditory Centers
Retrograde pathways have been demonstrated at each level of the
auditory nervous system from the cortex to the cochlea in the ear itself. The
final pathway is mainly from the superior olivary nucleus to the sound-receptor
hair cells in the organ of Corti.
These retrograde fibers are inhibitory. Indeed, direct stimulation
of discrete points in the olivary nucleus has been shown to inhibit specific
areas of the organ of Corti, reducing their sound sensitivities 15 to 20
deci-bels. One can readily understand how this could allow a person to direct
his or her attention to sounds of par-ticular qualities while rejecting sounds
of other quali-ties. This is readily demonstrated when one listens to a single
instrument in a symphony orchestra.