Pump Up the Volume: Could Excessive Neural Gain Explain Tinnitus and Hyperacusis?

Naturally occurring stimuli can vary over several orders of
magnitude and may exceed the dynamic range of sensory
neurons. As a result, sensory systems adapt their sensitivity
by changing their responsiveness or ‘gain’. While many peripheral
adaptation processes are rapid, slow adaptation
processes have been observed in response to sensory deprivation
or elevated stimulation. This adaptation process alters
neural gain in order to adjust the basic operating point
of sensory processing. In the auditory system, abnormally
high neural gain may result in higher spontaneous and/or
stimulus-evoked neural firing rates, and this may have the
unintended consequence of presenting as tinnitus and/or
sound intolerance, respectively. Therefore, a better understanding
of neural gain, in health and disease, may lead to
more effective treatments for these aberrant auditory perceptions.
This review provides a concise summary of (i) evidence
for changes in neural gain in the auditory system of
animals, (ii) physiological and perceptual changes in adult
human listeners following an acute period of enhanced
acoustic stimulation and/or deprivation, (iii) physiological
evidence of excessive neural gain in tinnitus and hyperacusis
patients, and (iv) the relevance of neural gain in the clinical
treatment of tinnitus and hyperacusis.