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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. Although severe hyperacusis is rare, a lesser form of hyperacusis affects musicians, making it difficult for them to play in the very loud environment of a rock band or orchestra which previously gave them no problems. It also makes attendance at loud discos or live events difficult for a portion of the population, given that sound levels at such events usually exceed recommended safe levels of exposure. This is a problem which may be caused by genetic differences, stress or ill-health, or by abnormal responses in the tensor tympani and stapedius muscles, which function in the normal acoustic reflex response that protects the inner ear from loud sounds. 40% of people with tinnitus report mild hyperacusis. ==Signs and symptoms== In cochlear hyperacusis (the most common form of hyperacusis), the symptoms are ear pain, annoyance, and general intolerance to any sounds that most people don't notice or consider unpleasant. Crying spells or panic attacks may result from cochlear hyperacusis. As many as 86% of people with hyperacusis also have tinnitus.〔 In vestibular hyperacusis, the person may experience feelings of dizziness, nausea, or a loss of balance when sounds of certain pitches are present. For instance, people with vestibular hyperacusis may feel like they are falling and as a result involuntarily grimace and clutch for something to brace themselves with. The degree to which a person is affected depends not only on the overall severity of that person's symptoms but also on whether the person can detect sounds in that frequency range at the volume in question, as well as on the person's preexisting muscle tone and severity of startle response. Anxiety, stress, and/or phonophobia may be present in both types of hyperacusis. Someone with either form of hyperacusis may develop avoidant behavior in order to try to avoid a stressful sound situation or to avoid embarrassing themselves in a social situation that might involve noise. A person with hyperacusis might be startled by very low sound levels. Everyday sounds like shutting doors, ringing phones, television, running water, ticking clocks, chewing gum, cooking, normal conversation, eating, dishes, and other sounds will hurt his/her ears. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hyperacusis」の詳細全文を読む スポンサード リンク
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