Closed-Loop Acoustic Stimulation Enhances Sleep Oscillations But Not Memory Performance

Abstract

Slow oscillations and spindle activity during non-rapid eye movement sleep have been implicated in memory consolidation. Closed-loop acoustic stimulation has previously been shown to enhance slow oscillations and spindle activity during sleep and improve verbal associative memory. We assessed the effect of closed-loop acoustic stimulation during a daytime nap on a virtual reality spatial navigation task in 12 healthy human subjects in a randomized within-subject crossover design. We show robust enhancement of slow oscillation and spindle activity during sleep. However, no effects on behavioral performance were observed when comparing real versus sham stimulation. To explore whether memory enhancement effects were task specific and dependent on nocturnal sleep, in a second experiment with 19 healthy subjects, we aimed to replicate a previous study that used closed-loop acoustic stimulation to enhance memory for word pairs. The methods used were as close as possible to those used in the original study, except that we used a double-blind protocol, in which both subject and experimenter were unaware of the test condition. Again, we successfully enhanced slow oscillation and spindle power, but again did not strengthen associative memory performance with stimulation. We conclude that enhancement of sleep oscillations may be insufficient to enhance memory performance in spatial navigation or verbal association tasks, and provide possible explanations for lack of behavioral replication.

The Treatment of Sleep Dysfunction in Neurodegenerative Disorders

“…Response rates appear variable; however, and in some studies, benefit was only seen when nonresponders were excluded (35% participants) [220]. As with TDCS, there are studies failing to demonstrate cognitive benefit within the literature, but these have typically also failed to show an overall increase in slow-wave activity following the intervention [223,224]. The precise stimulation protocol again appears critical, but in comparison with TDCS, efficacy to boost slowwave activity and benefit to cognition appears greatest when stimulation is phase-locked to the upstate of endogenous SOs [218,225,226]: so-called closed loop stimulation.…”

Selection of stimulus parameters for enhancing slow wave sleep events with a Neural-field theory thalamocortical computational model

“…A higher occurrence, or higher power of slow-wave events, may not be enough to enhance memory consolidation [30]. The relative timing of occurrence between SPs and SOs also play a role, with SPs being expected to be nested in the up-phase of a slow oscillation.…”

“…with STIM-R (see S1 Fig). A recent work [30] shows that this closed-loop stimulation pattern does not always enhance memory consolidation even with the increase of the power of the SWS events.…”

Effect of Closed-Loop Direct Electrical Stimulation during Sleep Spindles in Humans

“…With their protocol, the authors reported enhancement of both spindle activity and memory [11]. Several recent studies, however, challenged these previous results, reporting that increasing sleep oscillations may not always be sufficient to enhance memory performance [12,13].…”