The target of the letter, a study by Ahmadi and colleagues, took advantage of a randomized clinical trial to ask a deceptively simple question. When older adults undergo CBT-I and their sleep improves, does the electrical signature of their deep sleep change as well, and do those changes move in lockstep with improvements in memory performance? Slow-wave activity, the high-amplitude, low-frequency oscillations that dominate the electroencephalogram during the deepest stages of non-rapid eye movement sleep, has long been implicated in memory consolidation. The idea that restoring more robust slow waves in people with insomnia could restore some of the memory difficulties that accompany poor sleep is an attractive one, and testing it in a controlled trial setting represents an important step beyond cross-sectional surveys that can only show correlations at a single point in time.

The theoretical backdrop here is decades of work on sleep-dependent memory consolidation. During slow-wave sleep, the hippocampus, which acts as a fast, temporary store for newly learned information, is thought to replay recent memories in compressed bursts. These replays are coordinated with cortical slow oscillations, thalamic spindles, and hippocampal ripples, forming a nested hierarchy of rhythms that gradually redistributes labile memories into long-term cortical networks. In this framework, the depth and intensity of slow-wave activity serve as a kind of gauge of the brain’s overnight memory-processing capacity. Older adults typically show reduced slow-wave amplitude, and this reduction has been repeatedly associated with weaker overnight memory retention, which helps explain why the prospect of reversing it through insomnia treatment has generated so much interest.

CBT-I itself is the first-line treatment for chronic insomnia, recommended ahead of medication by clinical guidelines across the world. Rather than acting on brain chemistry directly, it works through behavioral and cognitive levers: stimulus control re-associates the bed with sleep rather than wakefulness and worry, sleep restriction consolidates fragmented nights into a denser block of sleep, and cognitive restructuring defuses the anxious beliefs about sleeplessness that keep the disorder alive. Systematic reviews and meta-analyses, including a 2024 component network meta-analysis by Furukawa and colleagues published in JAMA Psychiatry, have mapped which components and delivery formats work best in adults, and separate reviews have documented benefits in working populations. What has been less clear is whether the therapy’s effects reach beyond sleep itself, into the cognitive machinery that sleep is supposed to support.

This is precisely the territory that Zhang and Guo’s letter probes. A letter to the editor in a clinical journal typically does not present new data; instead, it scrutinizes the interpretation of published findings, and that interpretive role matters enormously for how results ripple outward into clinical practice and popular understanding. When a secondary analysis reports an association between slow-wave activity changes and memory improvement after CBT-I, the natural headline that follows is that better deep sleep drives better memory. The letter’s title, Reconsidering the sleep–memory link after insomnia therapy in older adults, signals that the authors believe the causal story may be more complicated, and that the field should resist collapsing a nuanced pattern of evidence into a simple before-and-after narrative.

There are good technical reasons for such caution. In a secondary analysis, the measures of interest were not necessarily chosen or timed with the sleep-memory question in mind, and the statistical power to detect a genuine brain-behavior association may differ substantially from the power needed to detect the trial’s primary treatment effect. Slow-wave activity is also notoriously variable, both within a single night and between nights, so a single laboratory recording before and after treatment may capture only a noisy snapshot of a person’s typical sleep architecture. Memory, meanwhile, is not a single faculty: episodic recall, working memory, and procedural skill can respond differently to sleep changes, and the specific tasks used in a trial shape which aspects of cognition are sensitive to improvement. Any of these factors can weaken or distort an observed correlation without invalidating the underlying science.

There is also the perennial problem of confounding in observational associations embedded within trials. If CBT-I reduces insomnia severity, depression, anxiety, or the sedating burden of hypnotic medications, all of these changes could plausibly improve memory test performance through routes that have nothing to do with slow waves. Conversely, slow-wave activity might increase simply because sleep becomes more consolidated and less fragmented, without any direct enhancement of the memory-consolidation machinery. In that scenario, slow-wave activity would function as a marker of improved sleep quality rather than as the mechanism by which memory improves, and interventions aimed specifically at boosting slow waves might then fail to deliver the cognitive benefits that patients and clinicians would expect. Distinguishing a biomarker from a mechanism is one of the hardest problems in sleep neuroscience, and it is exactly the kind of distinction that a well-aimed letter can force the field to confront.

None of this diminishes the value of the original investigation. Randomized clinical trials of CBT-I that collect overnight electroencephalography are rare and resource-intensive, and secondary analyses that mine them for mechanistic insight are a legitimate and often productive strategy. Work in other age groups underscores why the question is worth pursuing: studies of sleep electroencephalogram oscillations and memory processing during childhood and adolescence, such as the 2023 analysis by Kurz, Zinke, and Born in Developmental Psychology, show that the relationship between sleep rhythms and memory evolves across the lifespan, shaped by maturational processes that differ from those operating in aging brains. Findings from younger populations cannot simply be transplanted to older adults, whose slow waves are smaller, whose sleep is more fragile, and whose memory complaints may reflect heterogeneous underlying causes ranging from normal aging to early neurodegeneration.

The practical stakes are considerable. Millions of older adults live with chronic insomnia, and many of them also worry about memory. If treating insomnia reliably improved cognition, CBT-I would become not just a sleep therapy but a preventive intervention against age-related cognitive decline, a claim with enormous public health implications. But if the sleep-memory link after treatment is weaker, more conditional, or more indirect than early reports suggest, then overselling the cognitive benefits risks disappointment and misallocated expectations, even as the well-established benefits of CBT-I for sleep itself remain fully intact. Careful interpretive scrutiny, of the kind Zhang and Guo’s letter exemplifies, is therefore not a hostile act toward the original research but a necessary part of building an evidence base that can support confident clinical recommendations.

The episode also illustrates how science actually refines itself. A trial is run, a secondary analysis draws a mechanistic association, and colleagues elsewhere scrutinize the inference, prompting everyone to specify more precisely what the data do and do not show. The letter, published in Volume 22 of the Journal of Clinical Sleep Medicine with no declared competing interests and no external funding, joins a broader conversation that includes component-level meta-analyses of CBT-I and lifespan studies of sleep oscillations. The next steps that follow naturally from this exchange are larger trials with electroencephalography designed from the outset to test memory outcomes, repeated sleep recordings to average out night-to-night variability, and mediation analyses that can separate the effects of improved sleep quality from the specific contribution of slow-wave activity. Until those results arrive, the wisest reading is a measured one: CBT-I remains the gold standard for insomnia, deep sleep remains a compelling candidate mechanism for memory consolidation, and the precise thread connecting the two in older adults is still being carefully untangled.

Subject of Research: The relationship between slow-wave sleep changes after cognitive behavioral therapy for insomnia and memory function in older adults

Article Title: Reconsidering the sleep–memory link after insomnia therapy in older adults

Article References: Zhang, W., & Guo, X. (2026). Reconsidering the sleep–memory link after insomnia therapy in older adults. Journal of Clinical Sleep Medicine, 22(1), Article 137. https://doi.org/10.1007/s44470-026-00160-1

Image Credits: AI Generated

DOI: 10.1007/s44470-026-00160-1

Keywords: insomnia, cognitive behavioral therapy for insomnia, slow-wave sleep, memory consolidation, older adults, sleep electroencephalography, randomized clinical trial, sleep-dependent memory, aging brain, sleep medicine, episodic memory, cognitive aging