Does closed-loop auditory stimulation improve sleep and memory in people with chronic insomnia as it does in healthy adults?

Why a technique that works in healthy sleepers may not work in insomnia

CLAS works by playing short sounds timed to the rising phase of slow oscillations, the large, slow brain waves that characterize deep non-REM sleep. In healthy young adults, this can evoke more slow oscillations and sleep spindles—bursts of faster activity linked to memory—and in some studies deepen slow-wave sleep [5]. But the insomnia studies suggest that evoking the brain wave is not the same as improving the night. In the randomized crossover trial, CLAS did acutely increase slow-oscillation amplitude after stimulation, yet there was no beneficial effect on subjective or objective sleep or on declarative memory [1]. The pilot study likewise found an immediate increase in slow-oscillation amplitude and activity, along with reduced delta and spindle activity across the night, but no change in memory consolidation or sleep macrostructure [2].

One possible reason is that insomnia is not simply a case of too little slow-wave sleep. The pilot authors note a high variance in how well the automated stimulation worked, with many patients receiving only a small number of stimuli, and they conclude that stimulation protocols need optimization for clinical settings [2]. In other words, the same sound-timing approach that is calibrated for healthy sleepers may not fit the more fragmented sleep of people with insomnia.

What the insomnia trials actually measured—and what they found

The most direct evidence comes from two small crossover, sham-controlled studies in adults with chronic insomnia. In the 2025 randomized trial, 27 participants spent one night with CLAS and one with sham stimulation; memory was tested with a word paired-associate learning task, and sleep was assessed by morning questionnaire and polysomnography [1]. The 2024 pilot included 27 patients but analyzed only 17 who completed the study and met criteria, and only 7 of those received enough stimulation to evaluate the acute and whole-night effects [2]. Both studies found that CLAS was feasible and produced measurable changes in sleep brain waves, but neither found a consistent benefit for sleep quality, sleep structure, or declarative memory [1][2].

The 2025 trial also reported an association between an increase in slow-oscillation density during CLAS and fewer markers of sleep fragmentation, such as arousals [1]. That is a correlation, not proof that CLAS caused better sleep maintenance, and it hints that a subgroup of people with insomnia might respond differently. The authors explicitly suggest that some individuals may be more responsive to CLAS for sleep maintenance [1].

The healthy-adult evidence is real but does not guarantee a memory benefit

Even in healthy adults, the memory benefit is not automatic. In a study of 20 healthy young adults who took afternoon naps, CLAS delivered at slow-oscillation upstates disrupted sleep and evoked slow oscillations, spindles, and coupled slow-oscillation–spindle events, yet it failed to enhance motor procedural memory [3]. Participants improved after the nap regardless of stimulation, and that improvement correlated with the density of slow-oscillation-coupled spindles [3]. This suggests that the memory benefit depends on preserving sleep continuity and on precisely targeting the right phase, not merely on delivering sounds [3].

A separate study in 12 healthy young adults found that different sound types—pink noise, pure tones, and spoken vowels—could all trigger slow oscillations, with pink noise producing the most pronounced response, and that varying sounds may partly counteract habituation [5]. That work is about optimizing the sound signal itself, not about whether CLAS improves memory in insomnia, and it did not include people with chronic insomnia [5].

What this means if you have chronic insomnia

For now, the answer to the practical question is no: in the studies that directly tested CLAS in chronic insomnia, it did not reliably improve sleep or memory after a single night, even though it changed sleep brain waves [1][2]. The evidence is early—both insomnia studies were small, and the pilot analyzed only seven patients with sufficient stimulation [2]. A 2025 randomized placebo-controlled trial of a home-based closed-loop phase-locked auditory stimulation system in chronic insomnia reports improvements in sleep parameters without cognitive side effects, but the available abstract is too incomplete to judge the size, durability, or memory results of that trial [4]. Until more complete results are available, CLAS should be viewed as an experimental approach that can be delivered in insomnia but has not yet been shown to deliver the sleep and memory benefits seen in some healthy-adult studies.

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