Pink Noise Enhances Sleep and Memory

An acoustic device may be able to accomplish for older adults what sleeping pills still cannot: enhance both sleep and memory.

Researchers at Northwestern University in Chicago conducted a study of 13 healthy older adults whose sleep deepened and whose recall of word pairs improved with timed acoustic stimulation at night. The discovery holds promise not just for older people with insomnia but also for everyone concerned about aging and memory impairment.

Sleep may be deeper and memory better by listening to timed exposure to pink noise at nightAn acoustic device may be able to accomplish for older adults what sleeping pills still cannot: enhance both sleep and memory.

Researchers at Northwestern University in Chicago conducted a study of 13 healthy older adults whose sleep deepened and whose recall of word pairs improved with timed acoustic stimulation at night. The discovery holds promise not just for older people with insomnia but also for everyone concerned about aging and memory impairment.

Older Research on Deep Sleep and Memory

Previous research has shown that memory consolidation for facts and events takes place mainly during deep, or slow wave, sleep. Overnight new memories are replayed in the brain and processed so they become more resistant to loss and deterioration. In this way, sleep actually improves our mental hold on learning that took place the day before.

Research has also shown that gentle sound stimulation at night—pink noise, specifically, which sounds like rushing water—can increase slow wave activity and improve the recall of words. Three prior studies were conducted on young adults, all with positive results. The Northwestern team wanted to see if older adults, who typically get less deep sleep and whose risk of memory impairment is greater, would reap the same benefits.

How They Conducted This Study

Thirteen adults ages 60 to 84 participated in this randomized controlled study. They spent two nights in a sleep lab spaced one to two weeks apart.

The procedure on both nights was identical in the eyes of the participants. They wore a device consisting in part of an electrode cap that would record their brain activity as they cycled through the different stages of sleep.

About 90 minutes before bedtime, participants were shown a series of 88 word pairs on a computer screen and told to memorize the pairs. Then, in random order, they were shown one word and asked to recall the other half of the pair (e.g., energy: oil). Then they put on soft headphones and went to sleep.

An hour after waking up, each participant was again shown the words, in random order, and asked to recall the paired word.

What participants did not know was on which of the two nights they were going to be exposed to several pulses of pink noise during slow wave sleep. The noise wasn’t loud enough to wake them up; nor was it faint enough for their brains to tune out. There was no noise exposure on the other night.

A Relationship Between Pink Noise, Sleep, and Memory

The results of the study were similar to results in the studies of young adults. Although participants’ overall sleep structure did not change,

  • When acoustic stimulation was delivered, it increased slow wave activity in the brain.
  • The acoustic stimulation improved participants’ morning recall of words. As predicted, they remembered more words in the morning than they had the night before. But after acoustic stimulation, on average they remembered 9 more words than they had the night before, as compared with recall on the morning following the night without noise, when on average they remembered only 3 more words.
  • The relative change in slow wave activity predicted the improvement in memory.

Tracking Brain Activity to Time Noise Exposure Right

This study might lead to the conclusion that older adults could sleep more soundly and smarten up by using pink noise sound apps at night. Maybe so and maybe not. Exposed to continuous low-level sound, the brain might decide to tune it out.

The beauty of this new device lies in the way it individualizes and maximizes the effects of treatment. It uses an automated algorithm to monitor slow waves produced in the brain and deliver acoustic stimuli at just the right time. This feature—called a phase-locked loop—was found in previous studies to increase slow wave activity and memory consolidation in young adults during daytime naps. So despite age-related changes in sleep and memory (and whether or not insomnia is involved), older adults stand to gain a lot if and when the device comes to market.

Northwestern University currently has a patent pending but researchers say more testing is needed before the device is ready for general use. Still, it’s nice to know that some researchers studying sleep and memory are thinking outside the box.

White Noise for Quieter Nights

Some people say white noise helps them sleep. There are several more portable noise-masking options, ranging from pricey to inexpensive.

Absolute silence is what I need to fall asleep—or a close approximation. But insomnia sufferers like Jennifer, an insurance analyst, need white noise to nod off.

“I’m sensitive to noise when I’m trying to fall sleep,” she told me in an interview on the phone. “I keep the fan on so I won’t be distracted. I can’t go anywhere without my fan. I need it to block out other sounds.”

Fans are ideal for use in the summer: not only do they cool you off, but they can also cover up unpleasant noises like snoring, traffic, and TV. Like all machines that generate white noise, fans produce a constant sound composed of many different frequencies at uniform volume. They don’t drown out disruptive noise so much as mask it, creating background noise your brain tunes out.

But there are other more portable noise-masking options, ranging from pricey to inexpensive.

  • The Marpac Dohm is a round plastic device that measures 5 ¾ by 3 ¼ inches and weighs a pound and a half. Endorsed by the National Sleep Foundation, it has an internal fan that runs at two speeds, producing the sound of rushing air. The Dohm starts at $44.95.
  • At the high end, the Sound+Sleep Nomad weighs about a pound, costs $149.95, and comes equipped with 13 different “SoundStories,” including white noise, pink noise (more bass than white noise), brown noise (more bass still) and sounds recorded in the field, including the ocean, a meadow with chirping crickets, and a crackling flame. It automatically adjusts the volume of the sound track to mask ambient noise such as coughing or TV.
  • Much less expensive are the downloadable MP3 tracks offered by many companies on the Internet. Sound Oasis, for example, sells white noise, pink noise, and brown noise sound tracks that play all night and cost $4.99.
  • Simply Noise, on the other hand, sells an app available in the i-Tunes App Store for just $0.99. It’s called SimplyRain, for use with an iPhone or an iPad.
  • Finally, if the idea of wearing ear buds or ear phones all night is unappealing, my brother swears by his SleepPhones, wafer-thin speakers encased in a soft fleece headband he wears at night. Via tiny cables, the speakers plug into a CD player, MP3 player, or an iPod. They start at $39.95.

If you need background noise to fall asleep, which type of noise works best?