The Mechanisms of Tinnitus: Research Progress and Treatment Implications

Tinnitus, classically defined as the perception of sound that has no external source, and referred to by some as a phantom auditory perception, plagues as many as 50 million Americans, 12 million of them severely; and 2 to 4 million people are debilitated by it. For many years, progress toward effective treatments for tinnitus was hindered by an obscured understanding of its underlying physiologic mechanisms. Although tinnitus was presumed to be primarily a disorder of the ear, findings now are eliciting insights pointing to neurologic origins for tinnitus. Localization of brain activity is now possible by means of positron emission tomography (PET), single photon emission computer tomography (SPECT), functional magnetic resonance imaging (fMRI), and magnetoencephalographic studies (MEG). This research, coupled with intensive study in recently developed animal models, increasingly suggests that tinnitus is most commonly a disorder that can originate in the peripheral and/or central nervous system and brain, and can undoubtedly be triggered by injury to the ear.

Although there is no cure for tinnitus, research from around the world is probing tinnitus’s causes, potential therapies, and management. This intensive work is translating into successful tinnitus management: Up to 85% of treated patients cite a significant incidence of relief. But the perception of tinnitus is a very personal experience.

Tinnitus Components

Experts in tinnitus cite three major components of tinnitus: acoustic, affective, and motor response to the tinnitus sensation, all of which are attention-based. The three interact with each other to varying extents. For example, there is evidence that stress can worsen tinnitus and that tinnitus can interfere with a person’s ability to concentrate. There is also research concluding that tinnitus is caused by neural plastic changes, that there are regions of the brain where tinnitus-related activity has been identified, that there are clues regarding how hearing loss causes brain changes that underlie tinnitus, and that animal studies demonstrate that excessive sound stimulation causes chronic changes in neural activity in the auditory centers of the brain.

Experts recognize that the cascade of psychophysiologic and psychophysical mechanisms underlying tinnitus mandate a multidisciplinary approach incorporating a strong mind-body component. Otologic surgeons are now venturing to study stress, the brain function response, and consciousness. I never thought, as an otologist and ear researcher, that I would be getting involved in areas that border on behavioral neurology and the neuropsychological, said Abraham Shulman, MD, Director of the Martha Entenmann Tinnitus Research Center in Brooklyn, NY, who, with his group, including audiologist Barbara Goldstein, PhD, coined the term tinnitology. But that is where the study of tinnitus has led us.

Operative Theories: Changes

There are presently several competing theories on the origins of tinnitus, all pertaining to changes in the auditory system. The nature of those accompanying changes, however, is the subject of these operative theories.