(Nes/Getty Images)
Those who have never endured the relentless ringing of tinnitus can only dream of the torment. In fact, a bad dream may be the closest some get to experiencing anything like it.
The subjective sound, which can also be a hissing, buzzing, or clicking, is heard by no one else, and it may be present constantly, or may come and go.
Neuroscientists at the University of Oxford now suspect that sleep and tinnitus are closely intertwined in the brain.
Their findings hint at a fundamental relationship between the two conditions – one that has, surprisingly, been overlooked in the brain until very recently.
"What first made me and my colleagues curious were the remarkable parallels between tinnitus and sleep," neuroscientist Linus Milinski at Oxford's Sleep and Circadian Neuroscience Institute told ScienceAlert.
"Tinnitus is a debilitating medical condition, whereas sleep is a natural state we enter regularly, yet both appear to rely on spontaneous brain activity. Because there is still no effective treatment for subjective tinnitus, I believe that exploring these similarities might offer new ways to understand and eventually treat phantom percepts."
Watch the video below for a summary of the study:
https://www.youtube.com/watch?v=u_E59L1yCYI&t=1s
A 'phantom percept' is when our brains fool us into thinking we are seeing, hearing, feeling, or smelling something that is not there, physically speaking.
Many people only experience phantom percepts during sleep, but for around 15 percent of the world's population, an inescapable noise rings in their ears during waking hours, too.
Tinnitus is the world's most common phantom percept, and yet there is no known cause or cure, despite a long list of hypotheses.
While many individuals with tinnitus report poor sleep and show poor sleep patterns, the potential connection to this crucial bodily function has only recently come to light.
https://www.youtube.com/watch?v=kgIrfiyK4x8&t=1s
The Oxford researchers proposed that the large spontaneous waves of brain activity that occur during deep sleep, or non-rapid eye movement sleep (non-REM), might suppress the brain activity that leads to tinnitus.
To test that idea, the team turned to ferrets, which have a similar auditory system to humans. In experiments, published in 2024, researchers found that the ferrets that developed stronger tinnitus also showed disrupted sleep.
"We could actually see these sleep problems appear at the same time as tinnitus after noise exposure," Milinski told ScienceAlert. "This suggested, for the first time, a clear link between developing tinnitus and disrupted sleep."
Crucially, the ferrets that developed tinnitus showed overly responsive brain activity to sound. When the ferrets finally did manage to slip into non-REM sleep, that hyperactivity was dampened.
This suggests that sleep may temporarily mask the effects of tinnitus by engaging the same brain circuits.
"Our findings indicate that deep sleep may indeed help mitigate tinnitus and could reveal natural brain mechanisms for modulating abnormal activity," said Milinski.
Research on non-human animals has its obvious limitations, but the same sort of brain activity patterns may exist in humans, too.
Since their 2022 review, Milinski says the field has rapidly expanded, with a growing number of large-scale studies investigating how sleep, the environment, and tinnitus interact – and not just in ferrets.
A graphic depicting the study's findings. More detail on brain regions involved is shown in Figure 1 of the paper.
(Milinski et al., Brain Comms., 2022)
"I hope this research will lead to greater awareness of tinnitus and open new ways of exploring treatments," Milinski told ScienceAlert.
"Acknowledging the impact of tinnitus, especially in older adults, where hearing loss and tinnitus can increase isolation and contribute to mental health problems, is incredibly important."
Just this year, a study from China found that individuals with tinnitus were less able to suppress the hyperactivity of their awake brains as they transitioned into a sleep state.
During deep sleep, however, the hyperactivity linked to tinnitus was suppressed.
"This study establishes sleep as a critical therapeutic target to interrupt the 24-hour dysfunctional cycle of tinnitus," the authors conclude, led by Xiaoyu Bao of South China University of Technology.
At Oxford, Milinski and his colleagues are now focusing on how sleep may impact the development of tinnitus itself.
"Tinnitus can make sleep worse, and poor sleep may, in turn, make tinnitus worse. It may be a kind of vicious circle, although I do not believe it is unbreakable," speculates Milinski.
"When we do not sleep well, we become more vulnerable to stress, and stress is one of the strongest factors known to worsen tinnitus. Stress can even trigger tinnitus to begin with."
Further research could not only lead to effective tinnitus treatments, it may help scientists better understand the mysteries of sleep itself.
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