13 May 2015
The causes of tinnitus are largely unknown,, but the condition remains fairly common, especially among veterans. In some instances, it can be attributed to exposure to loud noises but some people still have it without any clear trigger.
Although most people with the condition, which is characterised by hearing ringing or noise when there is no actual sound, can cope, in some cases it can be debilitating.
An international team of researchers from the University at Buffalo (UB), Southeast University in Nanjing, and Dalhousie University in Nova Scotia, have made a major breakthrough that could lead to improved treatment.
Their work provides new insights into how tinnitus, and the often co-occurring hyperacusis, a condition that causes sounds to be perceived as intolerably loud, might develop and be sustained.
Published in the forthcoming edition of eLife, the study suggests that the neural network responsible for the perceived sound is more extensive than previously thought.
It is hoped that their findings could lead to a testable model that helps to identify what region or regions of the brain might be responsible for causing the two conditions. Having constructed a broader, more comprehensive neural network, the researchers hope to use the model by deactivating specific areas of the neural network.
Through trial and error, the team should be able to learn whether shutting down certain regions could relieve tinnitus, hyperacusis or both conditions.
Until a few decades ago, it was thought that tinnitus was a problem in the ear, until patients reported hearing the ringing in their deaf ear.
"This changed the thinking in the field," says Richard Salvi, director of UB's Center for Hearing and Deafness, and one of the study's authors. "Having severed the neural connection between the ear and the brain, it's impossible for the phantom sound to be generated in the ear. It has to be generated in the brain."
Although research hasn't been able to pinpoint the exact location of the brain that tinnitus affects, functional MRI studies have shown it triggers abnormal activity in multiple areas of the brain and actually involves a neural network.
In their latest research, the team replicated tinnitus in the lab and saw that certain brain regions became very active once the condition is triggered. By tracing the network's course, the investigators identified a major hub within the central auditory pathway, the sound processing center of the brain.
"Other research has shown this activity, but what is novel about the current study is the amygdala pops up. This is the part of the brain that assigns emotion to our perceptions," says Dr Salvi.
He said the team were shocked to see the auditory system of the brain connecting sound to the ear.
Dr Salvi said: "Almost all parts of the network can be explained: location of sound; the emotional attachment; why people get aroused when they have tinnitus; we're puzzled by the cerebellum involvement, but it might act like some kind of "gate" that's allowing the phantom sound to enter the consciousness."
Posted by Edward Bartel
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