Pink Noise Synced With Brain Rhythm Enhances Deep Sleep
Gentle sound stimulation, such as the rush of a waterfall, synchronized to the rhythm of brain waves significantly enhanced deep sleep in older adults, report Northwestern University researchers. The sound stimulation also improved the older adults’ ability to recall words.
Deep sleep is critical for memory consolidation. But beginning in middle age, deep sleep decreases substantially, which scientists believe contributes to memory loss in aging.
The sound stimulation significantly enhanced deep sleep in participants and their scores on a memory test. Senior author Phyllis Zee, professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine sleep specialist, said:
“This is an innovative, simple and safe non-medication approach that may help improve brain health. This is a potential tool for enhancing memory in older populations and attenuating normal age-related memory decline.”
Slow Wave Sleep Enhancement
13 participants 60 and older received one night of acoustic stimulation and one night of placebo stimulation. The sham stimulation procedure was identical to the acoustic one, but participants did not hear any noise during sleep.
For both the sham and acoustic stimulation sessions, the individuals took a memory test at night and again the next morning. Recall ability after the sham stimulation generally improved on the morning test by a few percent.
However, the average improvement was three times larger after pink-noise stimulation.
The older adults were recruited from the Cognitive Neurology and Alzheimer’s Disease Center at Northwestern. The degree of slow wave sleep enhancement was related to the degree of memory improvement, suggesting slow wave sleep remains important for memory, even in old age.
Although the scientists have not yet studied the effect of repeated nights of stimulation, this method could be a viable intervention for longer-term use in the home, Zee says. Previous research showed acoustic simulation played during deep sleep could improve memory consolidation in young people. But it has not been tested in older adults.
Real-time Brain Waves
The new study targeted older individuals, who have much more to gain memory-wise from enhanced deep sleep, and used a novel sound system that increased the effectiveness of the sound stimulation in older populations.
The study used a new approach, which reads an individual’s brain waves in real time and locks in the gentle sound stimulation during a precise moment of neuron communication during deep sleep, which varies for each person. During deep sleep, each brain wave or oscillation slows to about one per second compared to 10 oscillations per second during wakefulness.
Giovanni Santostasi, a study coauthor, developed an algorithm that delivers the sound during the rising portion of slow wave oscillations. This stimulation enhances synchronization of the neurons’ activity.
After the sound stimulation, the older participants’ slow waves increased during sleep. Larger studies are needed to confirm the efficacy of this method and then:
“the idea is to be able to offer this for people to use at home,” says first author Nelly Papalambros. “We want to move this to long-term, at-home studies.”
The study was funded by the Center for Circadian and Sleep Medicine in the Feinberg School of Medicine and an Alzheimer’s Disease Core Center grant from the National Institute on Aging to Northwestern University, Chicago Illinois.