Centrifugal control in mammalian hearing.

1. Centrifugal control of many sensory systems is well established, notably in the gamma motorneuron of skeletal muscle stretch receptors. 2. Efferent (olivocochlear) innervation of the mammalian cochlea was first established through anatomical studies. Histological studies confirmed synaptic terminals in contact with hair cells and afferent dendrites. 3. Electrophysiology has elucidated the cellular mechanisms of efferent modulation in the cochlea. 4. The system has potential roles in noise protection, homeostatic feedback control of cochlear function and signal processing. There is some evidence in support of each, but also contraindications. 5. It is concluded that the role of the olivocochlear innervation is still contentious but, on balance, the evidence appears to favour a role in enhancing signal detection in noise.