If you're one of the 50 million Americans who experience the constant ringing of tinnitus – or you just live in a noisy house or apartment and find it hard to get a good night's sleep – you might be familiar with white noise generators.
These devices emit a sound like the buzz of old-fashioned TV static, which can mask things like disruptive background noises and the ringing, high-pitched whine caused by tinnitus. But according to a new study, that's not all white noise might be doing to your brain.
"In the past 50 years, brain scientists have learned a great deal about brain plasticity - how sensory and other inputs change the brain chemically, structurally, and functionally," explains cognitive scientist Mouna Attarha, formerly a PhD student at the University of Iowa, and now a researcher at Posit Science Corporation, which makes brain training software.
"Increasing evidence shows that the brain rewires in a negative manner when it is fed random information, such as white noise."
In a new review article, Attarha and researchers from the University of California, San Francisco suggest that the background buzz of white noise – which some advocate as a means of lessening the perceived symptoms of tinnitus – could actually be harmful to our central auditory system.
While the biological mechanisms behind tinnitus aren't fully understood, scientists are continually finding evidence that the symptoms are tied to measurable changes in various parts of the brain that go beyond simple hearing loss – although tinnitus, especially when it first appears, is often associated with exposure to loud, traumatic noises that damage the eardrum and hearing.
While there's isn't significant evidence in humans to suggest that lower-volume sound like background white noise could bring about these kinds of changes in the central auditory system, Attarha's team cite animal studies that suggest prolonged exposure in animals does affect their brains.
"A rapidly growing body of literature, largely conducted in animal models within the last decade, has now established that long-term exposure to nontraumatic noise … is capable of inducing maladaptive plastic reorganisation of the central auditory nervous system in ways that bear striking phenomenological overlap with the persistent, widespread disinhibition of the auditory system thought to underlie tinnitus in humans," the authors write in their paper.
"Notably, these changes have been observed following exposure to noise levels in the 60 to 70 dB sound pressure level range, typical of commercially available noise generators and considered 'safe' by the US Occupational Safety and Health Administration."
According to the researchers, the putative neural effects on the central auditory system are numerous, but include a reduction in neural inhibition (the ability to filter unimportant information), a lengthening of the amount of time it takes for the brain to process changing signals, and less precise cortical representations (how information is represented in the brain).
It's far too early to conclude that the unstructured sound of white noise – a random combination of different frequencies – is having the same effects on people.
And it's also worth noting that two of the researchers have positions at Posit Science Corporation – developing commercial technology they say can have beneficial effects on cognitive processes, which is a disclosure to bear in mind in light of the ideas they're putting forward.
But nonetheless, given sound therapy with white noise is already being used to ostensibly help patients manage the symptoms of their tinnitus, the researchers say we should at least be open to the hypothetical possibility of the potentially harmful effects seen in animal studies.
Especially since, in their (unproven) hypothesis, that continued exposure to prolonged, low-level noise could be aggravating their condition, not helping it.
"Controlled neurobiological experiments investigating non-traumatic noise exposure thus suggest that sound therapies implementing broadband noise may be driving patients' brains further toward, rather than away from, the pathological disinhibitory state that has long been associated with tinnitus," the researchers write.
The findings are reported in JAMA Otolaryngology – Head & Neck Surgery.