The background sound-masking effects of white noise are well known. Regular travellers wear white noise headphones to block out the hubbub on a packed aeroplane, while light sleepers and parents with newborns invest in white noise machines to stop outside sounds from waking them or the baby up.
While white may be the most well-known noise frequency colour, new research at the Massachusetts Institute of Technology has found that pink noise may not only help us to sleep better, but also help us sleep to healthier.
“During the day, waste products such as lactic acid and worn-out proteins build up in the brain. When we sleep at night, waves of cerebrospinal fluid (CSF) help to wash away this waste, keeping the brain healthy,” says MIT News about the research.
“In a new study, MIT researchers have shown that they can strengthen these CSF waves through exposure to short bursts of a gentle, staticky sound known as pink noise during sleep,” the post continued. “These bursts increase the amplitude of slow electrical waves in the brain, which then enlarges the CSF waves.”
Researchers believe the study could have far-reaching implications, not only for boosting cognitive function, improving memory and aiding more restorative sleep, but also in slowing the progression of neurodegenerative diseases caused by the build-up of harmful proteins, such as Alzheimer’s, Parkinson’s, Huntington’s and Creutzfeldt-Jakob.
What are colour noises and what do they do?
Colours describe how sound energy is distributed across frequencies, from low-pitched rumbles to high-pitched hisses. “They are labels for the physical properties of a signal, rather than separate modes of brain activity,” says psychologist and neuroscience and psychotechnology researcher Nargiza Noimann-Zander.
“White noise has approximately equal power per hertz across the frequency range being considered. It has the familiar hiss of radio static. Pink noise contains relatively more low-frequency energy, with approximately equal power in each octave, so it usually sounds less sharp,” she adds.
Each colour noise has its own distinct sound and use. White noise is usually described as sounding like television or radio static and is used to mask background sounds, while brown noise sounds like heavy rainfall and has been linked to improved concentration.
Grey and violet noises are used to manage hearing conditions like tinnitus, sounding like a powerful waterfall and steam escaping a pipe, respectively, while blue noise sounds like the hiss of an aerosol spray can and is used to cover sharp environmental noises like sirens or traffic.
Green and black noises promote calmness, with green sounding like a rushing river and black representing near-total silence. Pink noise has been described as wind rustling through leaves or waves washing up on a beach and has traditionally been used to promote deep sleep and improve memory.
“Think of sound as being made up of lots of different frequencies, from low-pitched sounds to high-pitched ones,” says Dr Ash Shishodia, psychiatrist and neuropsychiatrist at Thrive Wellbeing Centre.
“Different types of noise contain different proportions of those frequencies. So, despite the colourful names, we are not talking about different types of ‘noise’ in the everyday sense. We are talking about different ways of arranging sound frequencies.”
What are the possible benefits of pink noise?
When waste proteins stay in the brain, they build up and form harmful clumps that damage brain cells and lead to memory loss and brain diseases. The brain’s natural “washing system”, called the glymphatic system, flushes them out while we sleep; however, the process fails to work as efficiently in those who regularly don’t achieve a state of deep sleep.
The MIT study found that 50-millisecond bursts of pink noise delivered at the peak of the brain’s slow waves stimulated blood vessels, causing them to constrict and dilate and creating a pump-like effect that pushed CSF out of the brain along with waste proteins.
Since its discovery in 1925, pink noise has been linked to improved focus, concentration and sleep, while recent research has been done in connection with its effects on those with Attention Deficit Hyperactive Disorder (ADHD).
“For concentration, individual differences are important,” says Ms Noimann-Zander. “A systematic review found small benefits from white or pink noise on some laboratory attention tasks in people with ADHD or high levels of ADHD symptoms. People without those characteristics did not show the same benefit, and performance could be worse. That is more specific than saying that noise improves concentration.”
But a more useful question is understanding what the person is trying to achieve, adds Dr Shishodia. If the aim is to relax, personal preferences are likely more important to allowing the mind and body to switch off, for example. If the goal is to mask intermittent environmental sounds, a steady broadband noise may be more fitting.
“And if the sound is loud enough to be uncomfortable, it defeats the purpose and potentially creates a hearing risk,” says Dr Shishodia. “The simplest rule is: if a background noise helps you, keep it comfortable and keep the volume low.”
