The Role of Auditory Deprivation

Hearing loss is the most important factor in the development of tinnitus. This chapter describes the changes that occur in the central auditory system as a consequence of hearing loss. Deprivation of input to the auditory system can cause two types of functional changes: it can alter the balance between inhibition and excitation, and it can activate neuronal plasticity. Any type of hearing loss, such as conductive or sensorineural hearing loss, results in decreased input to the central auditory nervous system. Noise-induced hearing loss is an example of auditory deprivation and overuse, which in turn can activate neural plasticity. An altered balance between inhibition and excitation can change the gain in the central auditory system. If the gain is increased, this can lead to hyperactivity in the form of tinnitus. The effects on the balance between inhibition and excitation may subside when normal input to the auditory system occurs. However, activation of neuronal plasticity that may occur as a result of sensory stimulation may persist even after normal sensory stimulation is restored. Plastic changes may become permanent, and reversal of neuronal plasticity may require special measures.