In a new study published in Trends and Cognitive Sciences, researchers say they have identified the defects in the brain that lead to tinnitus and chronic pain. The team hopes the findings will be the first step to developing therapies for these common complaints.
The authors of this new research - from Georgetown University Medical Center (GUMC) in Washington, DC, and Technische Universität München (TUM) in Germany - explain that the mechanisms in the brain that would usually control noise and pain signals lose the ability to do so, which in turn leads to a perception of noise or pain long after the initial injury occurred.
They describe these controls as a kind of "gate."
The scientists were able to follow the flow of these signals through the brain and show where controls should be occurring.
The brain "reorganizes" itself in response to injury, which is how Prof. Josef Rauschecker, director of the Laboratory for Integrative Neuroscience and Cognition at GUMC, describes it.
Tinnitus can follow when the ears are damaged by loud noise, something the brain continues to "hear." In a similar way, chronic pain from an injury can remain inside the brain long after the injury has healed.
"Some people call these phantom sensations, but they are real, produced by a brain that continues to 'feel' the initial injury because it cannot down-regulate the sensations enough," says Prof. Rauschecker. "Both conditions are extraordinarily common, yet no treatment gets to the root of these disorders."
The areas of the brain that are responsible are the nucleus accumbens and several areas of the prefrontal cortex and the anterior cingulate cortex.
Prof. Rauschecker explains that "these areas act as a central 'gatekeeping system' for perceptual sensations, which evaluate the affective meaning of sensory stimuli, whether produced externally or internally and modulates information flow in the brain. Tinnitus and chronic pain occur when this system is compromised."
The researchers also found that depression and anxiety and uncontrollable or long-term stress, all modulated by the nucleus accumbens, operate in close synchronicity with tinnitus or chronic pain, or with both together.
The very brain plasticity that produces some of these effects, the researchers add, suggests that the proper gatekeeping controls could be restored.
Dr. Markus Ploner, PhD, a consultant neurologist and Heisenberg professor of human pain research at TUM, says:
"Better understanding could also lead to a standardized assessment of individuals' risk to develop chronic tinnitus and chronic pain, which in turn might allow for earlier and more targeted treatment."
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