Ringing Ears: The Neuroscience of Tinnitus @ McMaster University

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Tinnitus, that phantom ringing in the ears that affects thousands in Canada, is generated not by the ear, but by neurons firing in the brain, according to a North American research team that includes a McMaster University scientist.

“The tinnitus is not generated by processes in the ear, but changes in the brain when hearing loss occurs,” said McMaster professor emeritus Larry Roberts, with the department of psychology, neuroscience, and behaviour.

Neurons, he said, are meant to talk to each other. When the ear stops talking to them, usually because of hearing loss, they start talking to themselves and this in turn, generates the ringing. “The sound is generated by neuron activity.”

Roberts said the conclusion is the result of collaborative work in the past decade, but said many people are not aware it’s the neurons, or changes in the brain producing tinnitus. Now the question is: how is the noise generated in the brain? “What are the neurons doing, and where are they doing it?” he said. “Our work will assist.”

Understanding how it happens might lead to finding a treatment. The findings also help scientists understand why tinnitus is such a difficult problem to treat, he added.

They also point to the importance of prevention.

About 300,000 to 350,000 people in Canada, or about one to two per cent of the population, suffer from severe tinnitus. About 10 to 12 per cent of all Canadians have some form of tinnitus, he said.

Peter Austen, acting president of the Tinnitus Association of Canada, has suffered from a severe form for five years and says he’s researched everything and tried everything. He says it’s long been known that tinnitus is a phantom noise generated in the auditory cortex in the brain.

The main problem with tinnitus, he believes, is that people are trying to find cures but none of what is out there will help.

“There’s no cure. Only management,” he said.

“You never want to get it. Don’t ever go to a concert without wearing earplugs,” he warns. “Teenagers don’t realize what they’re doing to themselves.”

Roberts said although tinnitus is most common after age 60, chronic tinnitus can happen at any age and it is a major cause of disability in soldiers returning from Afghanistan and Iraq.

Studies show hearing loss among young people is increasing and this may also lead to an increase in tinnitus, he said.

“If there’s a price to be paid for listening to loud music, it’ll be later in life,” Roberts said Thursday before leaving for the annual Society for Neuroscience meetings in San Diego where he and the other researchers will present a symposium on their findings.

Roberts said U.S. data shows 12 to 13 per cent of adolescents have hearing impairments. With iPods so common and the use of ear buds almost universal, this is quite alarming because more children will be more susceptible to tinnitus as they grow older, he said.

J Neurosci. 2010 Nov 10;30(45):14972-14979.
Ringing Ears: The Neuroscience of Tinnitus.

Roberts LE, Eggermont JJ, Caspary DM, Shore SE, Melcher JR, Kaltenbach JA.

Department of Psychology, Neuroscience, and Behaviour, McMaster University, Hamilton, Ontario L8S 4K1, Canada, Departments of Physiology and Pharmacology and Psychology, University of Calgary, Calgary, Alberta T2N 4N1, Canada, Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois 62794-9230, Departments of Otolaryngology and Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109-5616, Department of Otology and Laryngology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts 02114-3096, and Department of Neurosciences/Head and Neck Institute, The Cleveland Clinic, Cleveland Ohio 44195.

Abstract

Tinnitus is a phantom sound (ringing of the ears) that affects quality of life for millions around the world and is associated in most cases with hearing impairment. This symposium will consider evidence that deafferentation of tonotopically organized central auditory structures leads to increased neuron spontaneous firing rates and neural synchrony in the hearing loss region. This region covers the frequency spectrum of tinnitus sounds, which are optimally suppressed following exposure to band-limited noise covering the same frequencies. Cross-modal compensations in subcortical structures may contribute to tinnitus and its modulation by jaw-clenching and eye movements. Yet many older individuals with impaired hearing do not have tinnitus, possibly because age-related changes in inhibitory circuits are better preserved. A brain network involving limbic and other nonauditory regions is active in tinnitus and may be driven when spectrotemporal information conveyed by the damaged ear does not match that predicted by central auditory processing.

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