January 13, 2011
Tinnitus: More Fears for Ringing Ears
(Ivanhoe Newswire) -- The 40 million people in the U.S. who suffer from the phantom ear sensations of tinnitus may have a bigger problem than they think. A new study conducted by neuroscientists at Georgetown University Medical Center (GUMC) shows that the condition, commonly thought of as a simple hearing problem, is truly the result of functional and structural changes in the brain.
Tinnitus occurs after one loses the ability to hear specific frequencies due to aging, exposure to extremely loud noises, or an accident. The GUMC researchers believe that the brain compensates for this loss by working to recreate sounds to replace the missing frequencies. This process turns to tinnitus when the limbic system of the brain, which regulates emotions and other functions, is unable to stop the replacement sounds from reaching the processing of normal conscious hearing.
"We believe that a dysregulation of the limbic and auditory networks may be at the heart of chronic tinnitus," lead researcher and neuroscientist Josef P. Rauschecker, Ph.D., was quoted as saying. "A complete understanding and ultimate cure of tinnitus may depend on a detailed understanding of the nature and basis of this dysregulation."
The researchers tested 22 people, half suffering from tinnitus, using functional Magnetic Resonance Imaging (fMRI). In the patients with tinnitus, the researchers noticed moderate hyperactivity in their brain's primary and posterior auditory cortices. Heavy hyperactivity was observed in an area called the nucleus accumbens, most notably when the person was exposed to sounds matching their lost frequencies. The nucleus accumbens is located in the corticostriatal circuit, a system which assists in reward evaluation, aversive reactions, and emotion.
"This suggests that the corticostriatal circuit is part of a general 'appraisal network' determining which sensations are important, and ultimately, affecting how or whether those sensations are experienced," Rauschecker was quoted as saying. "In this study, we provide evidence that these limbic structures, specifically the nucleus accumbens and the ventromedial prefrontal cortex, do indeed differ in the brains of individuals with tinnitus."
The functional lapses exhibited by these structures have been linked to mood swings as well as chronic pain. Rauschecker believes that they point to the brain's difficulty in processing "unwanted sensory signals."
The researchers believe that fully understanding tinnitus will first require understanding the ways in which the auditory and limbic systems work together to form perception.
Source: Neuron, January 2011