Scientists at Oregon Health & Science University say they have zeroed in on a kind of brain switch that can make people hear phantom ringing even when no sound is actually there. Working with mouse models, the team found that cranking up serotonin activity in a specific neural pathway made the animals behave as if they were hearing a steady tone. The results point to a precise circuit that may help explain why tinnitus becomes a constant companion for some patients.
The work, published April 20 in the Proceedings of the National Academy of Sciences, identifies a discrete serotonergic circuit that feeds into the brain’s auditory centers. According to the paper, overstimulating those neurons can push the brain into perceiving sound when none exists.
How the team tested the idea
To probe that circuit, researchers turned to optogenetics, using light delivered through thin fiber optics to fire serotonin-producing neurons, then watched how the animals reacted in a modified auditory startle test. When the pathway was switched on, mice acted as if they had tinnitus. When serotonin’s effects in that same circuit were blocked, the tinnitus-like responses dropped significantly. Those methods and findings are detailed by Medical Xpress.
What it could mean for people on antidepressants
Selective serotonin reuptake inhibitors raise serotonin levels across the brain, and the new study offers a plausible explanation for why some patients say their tinnitus worsens after starting those medications. Clinicians are being urged to pay close attention when patients report new or louder ringing, as reported by OregonLive.
"Our study suggests a delicate balance," co-senior author Laurence Trussell said, adding that it might be possible to develop drugs that steer serotonin toward some brain regions but not the auditory circuit, according to Oregon Health & Science University. The researchers also found that shutting down the circuit in mice eased tinnitus-like behavior, suggesting the effect could be reversible in principle.
How common is tinnitus?
Roughly 10 percent of U.S. adults, about 25 million people, have experienced tinnitus that lasted at least five minutes in the past year, according to the National Institute on Deafness and Other Communication Disorders. For many, it is an occasional nuisance. For others, it can interfere with sleep, concentration and mental health.
Takeaways and next steps
Trussell and colleagues stress that the mouse experiments do not deliver an instant cure, but they do highlight new targets for treatments that could block serotonin’s effects only in auditory circuits. The team plans additional studies to find more precise ways to hit that pathway. In the meantime, researchers recommend protecting hearing from loud noise and talking with prescribing physicians about any medication side effects, including worsening ringing, as noted by OregonLive.
