The Mechanisms of Tinnitus: Research Progress and Treatment Implications

The first theory is that in patients with tinnitus, there is an increase in neural activity in the auditory system. This theory, said James A. Kaltenbach, PhD, Professor of Otolaryngology at Wayne State University in Detroit, maintains that neurons are firing at a higher rate, similar to the way they respond when sound is presented. There is much supporting evidence for this theory from electrophysiological studies in animals and imaging studies in human subjects.

A second view maintains that an increase in neural synchrony in the brain underlies tinnitus. Tinnitus is hypothesized to be a dysynchronous signal that can arise anywhere in the peripheral and/or central nervous system and uses the auditory system to express its dysfunction.

A third view holds that tinnitus is caused by a reorganization of the frequency map or a change in frequency representation. When part of the input is removed from the cochlea, as often occurs when there is sensorineural hearing loss, the corresponding part of the auditory cortex adopts sensitivity to adjacent, still-intact frequencies. The result is an expanded representation of frequencies bordering on the damaged frequencies of hearing loss. Some investigators believe that overrepresentation or reorganization gives rise to the percept of tinnitus.

A fourth theory is based on postulated temporal changes in the firing of neurons in the auditory pathway.

Neuronal Activity Changes: Causes and Implications

It is generally believed that in subjects with tinnitus, the change in neuronal activity is caused by a shift in the balance of excitatory and inhibitory impulses.

First, research shows that damage to the inner ear, such as that resulting from noise or aging, is associated with a reduction in inhibitory transmitters, especially glycine (at the brainstem level) and γ-amino butyric acid (GABA, in the midbrain and auditory cortex). Depleting these inhibitory neurotransmitters thus causes a disinhibitory effect: Neural activity increases and leads to tinnitus.

The second component causing neuronal changes is the increase in excitatory neurotransmitters, most notably glutamate and acetylcholine, in some structures.

The implications of these changes have led to several avenues of exploration in developing tinnitolytic therapies.

Treating and Managing Tinnitus: Where Do We Go from Here?

A multimodal, multidisciplinary approach to treating and managing tinnitus is generally employed. Accurate diagnosis of the etiology and classification of tinnitus, its types and subtypes, as well as related conditions identified in evaluation, are imperative for appropriate and effective recommendations for care: Medical significance of the disorder varies according to the individual patient.