Uncovering the Neural Basis of Tinnitus: Using Laboratory Animal Models in Tinnitus Research

Subjective tinnitus is characterized by the perception of a sound which has no acoustic source in the environment. Often, this phantom sensation is described as a “ringing” or “buzzing” in one or both ears. Nearly all adults will experience tinnitus at some point in their life, albeit perhaps only for a short time, and most likely as a consequence of exposure to loud noise. For ~10% of the general population, however, tinnitus is a chronic condition that can lead to disturbance of sleep, difficulty concentrating and, in some cases, severe forms of depression, all of which can negatively affect one’s quality of life. Unfortunately for tinnitus sufferers, a lack of understanding of its neural basis has hindered efforts to devise completely effective treatments. Early theories of tinnitus speculated that its signals originated in the cochlea and propagated to the brain via the auditory nerve; however, this theory has been challenged because tinnitus often persists after the auditory nerve has been surgically transected. Moreover, support for a central generator of tinnitus has emerged from several neuroimaging and magnetoencephalography studies on tinnitus patients which have found that their brain activity is altered compared to that of non-tinnitus subjects, during both quiet conditions as well as in response to acoustic stimuli. At present, however, it remains difficult to conclude from such non-invasive studies to what extent each of the reported changes is responsible for the onset and persistence of tinnitus.