For memory to consolidate properly, deep sleep is critical. Deep sleep does however decrease substantially in middle age and scientists believe this contributes to memory loss in aging.
In new research done at Northwestern Medicine, scientists have found that gentle sound stimulation in time with the rhythm of brain waves enhanced deep sleep significantly in older adults. The sound used would typically be something such as the rush of a waterfall and it improved the older adult’s ability to recall words.
The sound stimulation enhanced deep sleep in participants considerably and improved their scores on a memory test.
Dr. Phyllis Zee, a Northwestern Medicine sleep specialist and professor of neurology at Northwestern University Feinberg School of Medicine, was the senior author of the paper. She explained although this is a simple, innovative and safe method that does not use medication, it may help improve brain health. As such, it is a potential tool for decreasing normal age related memory decline and improving memory in older populations.
Thirteen participants in the study, all 60 and older, were given one night of acoustic stimulation, followed by one night of mock stimulation. The procedure for the mock stimulation was identical to the real one, but participants did not hear any sound during sleep.
For both stimulation sessions, the participants took a memory test at night and again the next morning. After the mock stimulation, recall ability generally improved by a few percent in the morning test. The average improvement was however three times larger after pink noise stimulation.
The participants were all recruited from the Cognitive Neurology and Alzheimer’s Disease Center at Northwestern.
Zee noted that this method could be a practical intervention for longer-term use in the home, although the Northwestern team have not yet studied the effect of repeating the stimulation for more than one night. There was a direct correlation between the degree of slow wave sleep enhancement and the degree of memory improvement, indicating that slow wave sleep remains important for memory, even in old age.
Previous research with acoustic simulation played during deep sleep was not tested in older adults, but it was demonstrated that it could improve memory consolidation in young people. The new study used a novel sound system that increased the effectiveness of the sound stimulation in older populations. Older individuals have much more to gain from enhanced deep sleep in terms of memory improvement.
A new approach was used with this study. An individual’s brain waves were read in real time and the gentle sound stimulation was locked in during the exact moment of neuron communication during deep sleep. This is different for each person. During wakefulness, each brain wave or oscillation occurs at about ten per second compared to one oscillations per second during deep sleep.
An algorithm that delivers the sound during the rising portion of slow wave oscillations was developed by Giovanni Santostasi, a study coauthor. This stimulation improves synchronization of the neurons’ activity. The older participants’ slow waves increased during sleep after the sound stimulation.
Nelly Papalambros, a Ph.D. student in neuroscience working in Zee’s lab and the first author of the paper noted that in order to confirm the effectiveness of this method, larger studies are needed. She added that they want to move the research to long-term at-home studies, and that they hoped to offer this for people to use at home eventually.
Scientists at Northwestern are testing the acoustic stimulation in overnight sleep studies in patients with memory problems at this time. The aim is to determine whether acoustic stimulation can improve memory in adults with mild cognitive impairment.
Studies conducted previously in individuals with mild cognitive impairment have shown that there is possibly a link between their sleep and memory impairments.
The full peer reviewed study was published in the journal Frontiers in Human Neuroscience.