Hyperacusis

Hyperacusis (also spelled hyperacousis) is a health condition characterized by an increased sensitivity to certain frequency and volume ranges of sound (a collapsed tolerance to usual environmental sound). A person with severe hyperacusis has difficulty tolerating everyday sounds, some of which may seem unpleasantly or painfully loud to that person but not to others.

It can be acquired as a result of damage sustained to the hearing apparatus, or inner ear. There is speculation that the efferent portion of the auditory nerve (olivocochlear bundle) has been affected (efferent meaning fibers that originate in the brain which serve to regulate sounds). This theory suggests that the efferent fibers of the auditory nerve are selectively damaged, while the hair cells that allow the hearing of pure tones in an audiometric evaluation remain intact. In cases not involving aural trauma to the inner ear, hyperacusis can also be acquired as a result of damage to the brain or the neurological system. In these cases, hyperacusis can be defined as a cerebral processing problem specific to how the brain perceives sound. In rare cases, hyperacusis may be caused by a vestibular disorder. This type of hyperacusis, called vestibular hyperacusis, is caused by the brain perceiving certain sounds as motion input as well as auditory input.