Project 5

Effects of partial hearing loss on the brain’s control of inner ear function

THigher centres in the brain have been shown to modulate the function of the inner ear via descending (efferent) control systems. For example, we have demonstrated that electrical stimulation of the inferior colliculus causes a change in cochlear neural and hair cell activity that is consistent with activation of these efferent pathways. Various roles for efferent descending control in normal hearing have been postulated, ranging from homeostatic regulation of hair cell and nerve fibre function to enhancement of the detection of signals of interest in background noise. However, it is not known whether the action of descending pathways is altered by a pre-existing hearing loss, even though it is well known that peripheral hearing loss induces plasticity in central circuitry and levels of neurotransmitter expression. If such changes occur then they indicate that the effects of hearing loss have to include not just direct effects on auditory sensitivity, but changes in efferent modulation as well. This project will address this question by quantifying the effects of electrical stimulation of the inferior colliculus will be quantified in normal animals and in animals with a partial hearing loss created by prior loud noise exposure.