There is considerable evidence that expression of neural plasticity plays a central role in the development of the abnormalities that cause many forms of tinnitus. Expression of neural plasticity can change the balance between excitation and inhibition, promote hyperactivity, and cause re-organization of specific parts of the nervous system or redirection of information to parts of the nervous system not normally involved in processing of sounds (such as the non-classical, or extralemniscal pathways). The strongest promoter of expression of neural plasticity is deprivation of input, which explains why tinnitus often occurs together with hearing loss or injury to the auditory nerve.