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.