Study Objectives As slow-wave activity (SWA) is critical for cognition, SWA-enhancing technologies provide an exciting opportunity to improve cognitive function. We focus on improving cognitive function beyond sleep-dependent memory consolidation, using an automated device, and in middle-aged adults, who have depleted SWA yet a critical need for maximal cognitive capacity in work environments. Methods Twenty-four healthy adult males aged 35–48 years participated in a randomized, double-blind, cross-over study. Participants wore an automated acoustic stimulation device that monitored real-time sleep EEG. Following an adaptation night, participants were exposed to either acoustic tones delivered on the up phase of the slow-wave (STIM) or inaudible “tones” during equivalent periods of stimulation (SHAM). An executive function test battery was administered after the experimental night. Results STIM resulted in an increase in delta (0.5–4 Hz) activity across the full-night spectra, with enhancement being maximal at 1 Hz. SWA was higher for STIM relative to SHAM. Although no group differences were observed in any cognitive outcomes, due to large individual differences in SWA enhancement, higher SWA responders showed significantly improved verbal fluency and working memory compared with nonresponders. Significant positive associations were found between SWA enhancement and improvement in these executive function outcomes. Conclusions Our study suggests that (1) an automated acoustic device enhances SWA; (2) SWA enhancement improves executive function; (3) SWA enhancement in middle-aged men may be an important therapeutic target for enhancing cognitive function; and (4) there is a need to examine interindividual responses to acoustic stimulation and its effect on subsequent cognitive function. Clinical trial registration This study has been registered with the Australian New Zealand Clinical Trials Registry. “The efficacy of acoustic tones in slow-wave sleep enhancement and cognitive function in healthy adult males”. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=371548&isReview=true Registration ACTRN12617000399392.

No abstract

The human sleep-wake cycle is regulated by two processes which act primarily in opposition to consolidate sleep and wake (Borbély, 1982). Process S reflects the homeostatic accumulation and dissipation of sleep drive across wake and sleep, respectively, while Process C reflects the endogenous circadian modulation of alertness, promoting wake during the biological day and sleep during the biological night (Borbély, 1982). During the waking day, the circadian signal for alertness peaks during a 2-3 hr window of minimal sleep propensity prior to the evening onset of melatonin secretion, described as the wake maintenance zone (WMZ; Dijk et al., 1992;

Acoustic stimulation has been shown to enhance slow wave sleep and in turn, cognition, and now cardiac outcomes in young adults. With the emergence of commercial acoustic devices in the home, we sought to examine the impact of an acoustic, slow wave enhancing device on heart rate variability in healthy, middle-aged males (n = 24, 39.92 ± 4.15 years). Under highly controlled conditions, the participants were randomised to receive closed-loop brain state-dependent stimulation in the form of auditory tones (STIM), or no tones (SHAM), in a crossover design, separated by a 1 week washout period. STIM and SHAM were compared on measures of heart rate variability for the whole night and over the first three sleep cycles. We found an increase in slow wave activity following STIM compared with SHAM. There was a significant increase in high frequency power and standard deviation of the normalised RR-intervals (SDNN) during the STIM condition compared with SHAM (p < 0.05), due to changes observed specifically during N3. In conclusion, heart rate variability appears to improve following acoustic slow wave sleep enhancement.

No abstract