Introduction

Tinnitus is an auditory perceptual phenomenon that is defined as the conscious perception of internal noises without any outer auditory stimulation. The sounds may be very loud and bizarre and the most common ones are heard like a high-pitched musical tone, or a rushing sound like escaping steam, or air. Other descriptions can be more complicated such as metallic sounds, multiple tones of varying frequencies and mixtures between buzzing and ringing (see ‘Deafness and hearing loss’).

Tinnitus is in most cases a temporary sensation, which many people have experienced at least sometime in their life. However, it may develop into a chronic condition, and prevalence figures show that at least 10–15% of the general population have tinnitus (Davis & Rafaie, 2000). However, most cases of tinnitus are not severe. Only about 1–3% of the adult population has severe tinnitus, in the sense that it causes marked disruption of everyday activities, mood changes, reduced quality of life and disrupted sleep patterns. Tinnitus has been reported in children, but in its severe form, it is more common in adults and in particular in the elderly (see also ‘Ageing and health’ and ‘Noise: effects on health’).

Tinnitus is known to occur in association with almost all the dysfunctions which involve the human auditory system (Lockwood et al., 2002). This includes damage to the middle ear, the cochlea, the audiovestibular cranial nerve and pathways in the brain from cochlear nucleus to primary auditory cortex. A common distinction is often made between so-called objective (somatosounds, which can actually be heard from the outside) and subjective tinnitus (sounds that are heard only by the afflicted person).