Tinnitus – Current Neuroscience Research and Theories
By Bonnie O’Leary
If you struggle with tinnitus, you are not alone. There are over 46 million people in this country who have some form of this often debilitating condition. This tinnitus workshop was presented by Amber M. Leaver, PhD, who got involved with tinnitus research at Georgetown University’s Medical Center two years ago. I thank her for providing notes from her power point to assist us in our report.
Dr. Leaver began the workshop with some background on tinnitus. It is a common hearing disorder in which a person hears a “phantom sensation” of sounds in the ear – buzzing or ringing are the most common – even though no external sound is present. Tinnitus can come and go, it can bother us for long periods of time, or it can be present constantly. Groups at high risk for developing tinnitus include those who are exposed to loud noise: construction workers, musicians, and military personnel. More military veterans receive compensation for tinnitus and hearing loss than for any other medical issue.
Tinnitus can be associated with difficulty sleeping and fatigue, stress, anxiety, depression, and other factors.
Causes of tinnitus
The exact cause of tinnitus is unknown, but there are triggers to watch out for. The most common is exposure to loud noise and resulting hearing loss. Head or neck injury, temporomandibular joint/jaw dysfunction (TMJ), and certain drugs are other triggers. However, not everyone with hearing loss or head injury develops chronic tinnitus, and this is a phenomenon that neuroscience research is attempting to understand. To understand tinnitus, we need to understand how the brains of people with tinnitus are different from those without tinnitus.
How does tinnitus affect the brain? Currently, research identifies changes in two parts of tinnitus patients’ brains: the auditory system and the limbic system.
The auditory system begins in the ear, where sound is converted to neural impulses which travel to the auditory sensory processing center, or the auditory cortex. People with tinnitus have hyper-responsiveness to sound in their auditory cortex, especially sounds like their tinnitus sensation. In all people, the auditory cortex contains tissue that’s organized by what pitch it responds to best, like a keyboard on the brain. This is called tonotopy.
When we lose our hearing, these “brain keyboards” are missing “keys” corresponding to the hearing loss, and they also have extra “keys” corresponding to pitches close to their hearing loss. In tinnitus sufferers, these extra keys often match the tinnitus sensation, and it is thought that the imbalances in hyperactivity and tonotopy produce the tinnitus sensation. What is unclear is whether these changes are due to hearing damage or to tinnitus itself, making it hard to prove that changes to the auditory system alone cause tinnitus.
The limbic system is considered the emotional part of the brain, but it has also shown to be involved in deciding the value of our thoughts and behaviors. The limbic system seems to be different in people with tinnitus due to a section of the brain being structured differently than in people without tinnitus.
Similar differences in this part of the brain are found in people with depression and chronic pain. Dr. Leaver and her colleagues propose that this part of the limbic system works like a noise-cancellation system. When this system doesn’t work well, people are not able to suppress unimportant thoughts and perceptions – including phantom perceptions like tinnitus.
The impact of research on the development of treatments for tinnitus
As many of us know, there is currently no cure for tinnitus, and there is no treatment that works for everyone. It will be crucial to identify the brain basis of tinnitus to develop effective treatments. If the brain basis is mostly auditory, then treatments should target the auditory system. If, on the other hand, the brain basis is limbic, then treatments will have to target the limbic system.
To learn more, Dr. Leaver directed us to the website for the American Tinnitus Association, www.ata.org.