Examining the optimal timing for closed-loop auditory stimulation of slow-wave sleep in young and older adults

Abstract

Study Objectives Closed-loop auditory stimulation (CLAS) is a method for enhancing slow oscillations (SOs) through the presentation of auditory clicks during sleep. CLAS boosts SOs amplitude and sleep spindle power, but the optimal timing for click delivery remains unclear. Here, we determine the optimal time to present auditory clicks to maximize the enhancement of SO amplitude and spindle likelihood. Methods We examined the main factors predicting SO amplitude and sleep spindles in a dataset of 21 young and 17 older subjects. The participants received CLAS during slow-wave-sleep in two experimental conditions: sham and auditory stimulation. Post-stimulus SOs and spindles were evaluated according to the click phase on the SOs and compared between and within conditions. Results We revealed that auditory clicks applied anywhere on the positive portion of the SO increased SO amplitudes and spindle likelihood, although the interval of opportunity was shorter in the older group. For both groups, analyses showed that the optimal timing for click delivery is close to the SO peak phase. Click phase on the SO wave was the main factor determining the impact of auditory stimulation on spindle likelihood for young subjects, whereas for older participants, the temporal lag since the last spindle was a better predictor of spindle likelihood. Conclusions Our data suggest that CLAS can more effectively boost SOs during specific phase windows, and these differ between young and older participants. It is possible that this is due to the fluctuation of sensory inputs modulated by the thalamocortical networks during the SO.

Susceptibility to auditory closed-loop stimulation of sleep slow oscillations changes with age

“…Altered SO characteristics in older age may hence require different stimulation settings, that is, adapted timings for stimuli to occur at a particular phase “sweet spot” where greater enhancement could still be elicited. Accordingly, whether adjusting the delay between detected SO trough and stimulus application, as was done for our middle-aged adults to account for the delayed SO peak, helped or hindered stimulation effects, remains a subject for future investigations [ 50 ]. It is unlikely that the observed decrease in responsiveness to auditory stimuli during sleep in the older group could be attributed to an insufficient stimulation volume, as this was accounted for individually calibrating the volume to a level where visually identifiable evoked responses were elicited in the EEG.…”

Targeted memory reactivation of a serial reaction time task in SWS, but not REM, preferentially benefits the non-dominant hand

“…To fit threshold, a spindle had to be during stage N3 (SWS), be between 0.3 and 2.5 seconds long, and have at least 5 oscillations in that period. Spindle identity was then further confirmed by using time-frequency information to detect whether increased spindle-band power indeed took place during the selected segments (Purcell et al, 2017; Navarrete et al, 2020).…”

Exposure to relaxing words during sleep promotes slow-wave sleep and subjective sleep quality

“…Previous literature suggests that the processing of words is most effective during cortical up states, i.e. at the peaks of slow-waves [45][46][47] . A closed-loop setup could benefit word processing by targeting the presentation of words precisely in the up-states of slowwaves.…”