Tinnitus is a common medical symptom marked by a persistent ringing in ears, one which can be brought about through a number of different causes, including disease or injuries. Now, after mapping out the brain networks involved in producing the phantom sounds, researchers believe they know why the problem is so difficult to treat.
University of Iowa researchers employed a brain-monitoring technique usually used during surgery to treat epilepsy to map the process of tinnitus.
Investigators taking part in the study measured brain activity during bouts of tinnitus, comparing stronger and weaker occurrences of the condition. They also measured these results against brain patterns seen when the volunteers were exposed to a sound meant to mimic the symptom.
"Perhaps the most remarkable finding was that activity directly linked to tinnitus was very extensive and spanned a large proportion of the part of the brain we measured from. In contrast, the brain responses to a sound we played that mimicked [the subject's] tinnitus were localized to just a tiny area," said Will Sedley from Newcastle University in England.
The research suggests that tinnitus not only fills in the sounds missing after hearing damage, but also spreads into other areas of the brain. Tinnitus is the perception of a sound that is often described as ringing, but that isn't really there.
"This has profound implications for the understanding and treatment of tinnitus, as we now know it is not encoded like normal sound, and may not be treatable by just targeting a localized part of the hearing system," Phillip Gander from the Department of Neurosurgery at the University of Iowa said.
The University of Iowa is one of the few locations equipped to carry out such brain monitoring. Roughly one in five people suffers from some degree of tinnitus, but finding patients who are both undergoing epilepsy treatment with the invasive brain sensors and who suffer from tinnitus is difficult. A 50-year-old man who experienced ringing in both ears following hearing loss was examined in the study.
This study reveals new information on why tinnitus is so hard to treat. Because so many pathways in the brain are activated by the condition - not just those that "hear" the sound - it can be difficult for medicines or other treatments to reduce the symptom.
Neurofeedback, in which patients learn to control their brainwaves, is often utilized to control the persistent ringing. The condition is usually just irritating to people experiencing tinnitus, but in extreme cases, it can become debilitating. Many patients can suffer depression, anxiety and anger from continued ringing in their ears, which may be treated through drugs, psychological coaching, sound therapy or with hearing aids.
Study of brain pathways activated by tinnitus was detailed in the journal Current Biology.
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