'Pink Noise' Enhances Deep Sleep, May Improve Recall in Mild Cognitive Impairment

By Anne Harding

July 10, 2019

NEW YORK (Reuters Health) - Sound stimulation with "pink noise" enhanced deep sleep and improved recall for some patients with mild cognitive impairment, in a small pilot study.

"Our findings showed that auditory stimulation can enhance slow-wave sleep, or deep sleep, in people with mild cognitive impairment, who are at risk for Alzheimer's disease," Dr. Roneil G. Malkani of Northwestern University Feinberg School of Medicine in Chicago told Reuters Health by email. "We found that those people who responded better to the stimulation had better memory response."

Disrupted sleep may be a risk factor for amnesiac mild cognitive impairment (aMCI) and Alzheimer's disease (AD). People with aMCI spend less time in slow-wave sleep (SWS) and have reductions in sleep spindle count and density and slow-wave activity (SWA), Dr. Malkani and colleagues write in Annals of Clinical and Translational Neurology, online July 1.

The authors previously found that acoustic stimulation strengthened SWA and improved memory in cognitively normal older adults. In the new study, nine patients with aMCI underwent one night of acoustic stimulation and one night of sham stimulation. Before and after sleep, the researchers tested patients' declarative memory with a verbal paired-associate test.

Stimulation was phase-locked to the upstate of study subjects' sleep slow-waves, and consisted of 50-ms pulses of pink (1/f) noise in blocks of five (ON interval), followed by a 6-s pause (OFF interval).

Because the intensity (or amplitude) of pink noise decreases as its frequency increases, it's smoother and more soothing than white noise.

Slow oscillation (SO) activity increased by 15.1% during ON intervals compared to sham ON intervals, while SWA was 11.4% higher. Within-individual comparison of ON/OFF intervals showed an SO increase of 22.2% during stimulation, while SWA rose 17.9%, both significant increases.

Five participants performed better on the memory test after stimulation. Increase in SWA with stimulation was associated with better morning word recall. Individuals' amount of SWA enhancement was "highly variable," the authors note, and ranged from 1.4% to 29.8%.

Dr. Malkani and colleagues plan to conduct larger studies of the intervention, and investigate the effect of multiple nights of stimulation on memory.

"Although we reported data on only nine patients with mild cognitive impairment, we did see enhancement of slow waves and effects on memory with just one night of stimulation," Dr. Malkani said. "Our results show that people with mild cognitive impairment can still get memory benefits from sleep and that they have adequate brain plasticity to respond to auditory stimulation in sleep."

He added, "Given the links between slow-wave sleep and memory, our study has important implications for understanding the relationship between sleep, memory, and Alzheimer's disease. Furthermore, auditory stimulation has potential as a therapy in people with mild cognitive impairment."

One of the study's authors is scientific officer at Deep Wave Technologies, and two study authors are listed as inventors on a patent application filed by Northwestern University on the acoustic stimulation technique used in the study.

SOURCE: https://bit.ly/2xEJgpc

Ann Clin Transl Neurol 2019.

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