Effect of open-loop auditory stimulus during NREM sleep among youth & geriatric subjects: A comparative nap study

Background: Age-related sleep architecture alterations include fewer N2 sleep spindles, shorter N3 duration, and Slow Waves. This is linked to age-related decline in cognition. Auditory stimulation (AS) improves sleep oscillations. Aim: This study examines how open-loop AS impacts spindles and SW in young (YNG) and older (OLD) individuals during N2 and N3. Methods: A nap polysomnography was conducted on two healthy adult groups: YNG (n=8, 19–34 years) and OLD (n=6, 50–65 years). In N2 and N3 stages, a 20s AS was given, with 2s of 13.75 Hz modulated pink noise, 8s of constant pink noise, and 10s of no sound. Results: OLD demonstrated increased N2% (YNG = 49.53 ± 25.48, OLD = 84.86 ± 11.24, p = 0.043) and reduced N3% (YNG = 39.11 ± 28.47, OLD = 2.06 ± 4.33, p = 0.021) compared to YNG. OLD produced more spindles (YNG = 4.9 ± 2.14, OLD = 7.15 ± 1.47, f = 5.5, p = 0.036, η2 = 0.288) with lower amplitude (YNG = 52.13 ± 11.38, OLD = 39.9 ± 6.9, f = 5.37, p = 0.039, η2 = 0.3). AS increased SW counts in both groups (YNG = 6.9 ± 6.00, OLD = 0.901 ± 0.348, f = 5.48, p = 0.037, η2 = 0.304), with YNG having higher counts. Conclusion: AS increases spindles in OLD, enhanced amplitude in YNG, and SW count in both groups without altering frequency. These findings help us understand aging-related sleep alterations and differential effects of AS on spindle and SW activity.