Effect of Age on Fatiguing Characteristics of Efferent Inhibition

Abstract

Efferent nervous system is reported to protect the cochlea from noise induced damage, improves signal detection in noise and enhances the dynamic range. However, it is not clear as to whether such positive influences remain stable over continuous prolonged stimulations. The present study evaluated the effect of age and fatiguing characteristics of efferent system during prolonged acoustic stimulation. A total of 80 normal hearing subjects who were divided into 4 age groups, participated in the study. From each subject, TEOAEs were recorded four times after different duration of continuous stimulation. In each recording, the overall SNR as well as amplitude at each half-octave frequency were noted. The results showed that efferent fibers do not deteriorate during prolonged stimulation and also these fibers do not degenerate with advancing age. Degeneration of sensory cells and the afferent auditory neurons do not influence efferent inhibition. Hence, it is concluded that unlike afferent neurons, efferent neurons do not evidence degenerative changes in their physiology up to 60 years of age.