As we age, the quality of our sleep declines. We sleep less, often disturbed by noises with frequent awakenings and a prominent reduction in REM (rapid eye movement) sleep. This sleep deprivation often leads to memory loss in later years.
But researchers from North-western University in Evanston, Illinois have found a simple solution to this — it’s called “pink noise”.
Pink noise is the gentle soothing sound where each octave possesses equal energy. Pink noise is essentially background everyday noise which we hear in our environment.
Many studies have highlighted the importance of sleep for memory consolidation, which is the brain’s ability to convert short-term memory into long-term memories. Deep sleep, also known as slow-wave sleep (SWS), is considered particularly relevant for memory consolidation. But, as we get older, SWS can decrease and as such can have negative influences on memory as has been shown by previous studies.
While an association has been discovered between acoustic stimulation of slow-wave brain activity during sleep and improved memory in young adults, very little was known about using acoustic stimulation in older adults. That’s what this new study sought to examine.
For this study, the researchers recruited 13 cognitively healthy adults between the ages of 60 and 84 years. All participants underwent a research neuropsychological and neurological evaluation according to standardised data collection procedures and were determined to be cognitively normal for their age.
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Participants completed two overnight sessions which were at least one week apart. In one session, they were subjected to acoustic stimulations (STIM) and on another night they were subjected to inactive (sham) stimulation. The acoustic stimulation consisted of “pink noise” which was synced with their brainwaves while they slept. During the sham stimulation, there was no noise delivered even though it consisted of an identical setup with phase-locked loop tracking.
The order of the visits were randomised, which resulted in six participants receiving acoustic stimulation and seven receiving sham stimulation during their first visit. Participants were blinded to the condition at each visit. They arrived at the laboratory at six o’clock in the evening. 90 minutes before their self-reported bedtime participants completed a word pair learning task and a cued-recall test.
Participants were fitted with soft headphones specifically designed for sleeping. The intensity of the stimulation was adjusted to a level that the participant considered acceptable and would not disturb their sleep (30–50 dB).
Lights were turned off at the time reported by participants in a screening questionnaire. They were given at least eight hours of sleep during which polysomnography was performed. An hour after waking, participants completed the delayed cued-recall test.
To examine any differences in subjective feeling which might affect sleep quality, participants completed questionnaires on mood, alertness and sleep quality 45 minutes after waking.
The researchers found that memory recall improved during both types of stimulations but it improved three times greater with acoustic stimulation than sham stimulation. There was a 26 per cent increase in word pairs recalled following overnight acoustic stimulation compared to sham stimulation.
On analysing everyone’s sleep waves, researchers found that participants’ slow-wave oscillations increased when there were subjected to pink noise stimulation.
Researchers say that syncing pink noise to the brain waves of older adults while they slept resulted in a greater increase in the quality of SWS, enhancing their quality of sleep and improving their memory. This positive effect lies in the ability of the sound to stimulate slow wave sleep in older adults.
This study further emphasises how important deep sleep is for memory consolidation, even in later life.
Researchers believe that acoustic stimulation may be a way to boost sleep quality and improve memory in later years and it doesn’t have to be restricted to pink noise. All soothing sounds like music, sounds of nature and white noise is good and can have the same positive effect on sleep.
Source: Frontiers in Human Neuroscience.
