After attending a loud concert and retreating to the quiet solitude of your bedroom, you may feel your ears filled with a rushing, screeching, or ringing noise. This sensation, associated with hearing loss, is called tinnitus, and for decades scientists have been trying to understand how the ears can “hear” or create noise in the absence of sound, whether that’s caused by structural brain changes, depression, or hearing loss — or a combination of all three.
Now, a new study published in the journal Trends in Cognitive Sciences examines how the underlying factors in tinnitus are similar to those involved in chronic pain, offering new clues on how to treat both conditions. While tinnitus sufferers hear unpleasant sounds constantly, chronic pain patients (many of whom have had a limb amputated) can continue to feel pain from a body part that’s no longer there. This is called phantom pain, and it originates in the spinal cord and brain.
The study was conducted by a collaborating team of researchers from the Technical University of Munich (TUM) and Georgetown University Medical Center, and led by Professor Josef Rauschecker, director of the Laboratory for Integrative Neuroscience and Cognition at Georgetown University, who has been studying tinnitus for years.
In 2010, Rauschecker and a team of scientists proposed that tinnitus was possibly caused by the brain’s inability to “tune out” negative sensory signals — and his latest study builds upon that.
The researchers used an array of techniques to examine the amount of gray matter in the brain as well as brain function, including functional magnetic resonance imaging (fMRI), positron emission tomography, and voxel-based morphometry. They discovered that loss of gray matter, as well as impaired circuit function, in certain areas in the brain — referred to as “gatekeeping” areas — contributed to both tinnitus and chronic pain. This process is impacted by dopamine and serotonin, neurotransmitters that play a huge role in mood, depression, and energy.
“These areas act as a central gatekeeping system for perceptual sensations, which determines the affective value of sensory stimuli — whether produced externally or internally — and modulates information flow in the brain,” Rauschecker said in the press release. “Tinnitus and chronic pain occur when this system is compromised.”
Rauschecker has examined depression’s role in tinnitus as well — finding that in many cases, depression is the cause of tinnitus and not the other way around. Some severe tinnitus sufferers saw great relief in their symptoms after visiting a psychiatrist and learning mindfulness to embrace the noise — and they actually reported it lowered significantly.
“Better understanding [of tinnitus and chronic pain] might allow not only for early treatment, but also more targeted and individual treatment with existing as well as novel strategies, such as dopaminergic therapy,” Markus Ploner, an author of the study and a consultant neurologist at TUM, said in the press release.
Source: Rauschecker J, May E, Maudoux A, Ploner M. Frontostriatal Gating of Tinnitus and Chronic Pain. Trends in Cognitive Sciences. 2015.