Deep Sleep, Dementia, and the Brain: New Evidence Highlights Why Quality Sleep Matters

By Dr. Heather Read, Professor, University of Connecticut

In late March 2025, CNN reported on compelling new research linking the amount of deep and rapid-eye-movement (REM) sleep we get to the long-term health of our brains [1]. The study, led by researchers at Yale, found that middle-aged adults who spent less time in slow-wave sleep (deep N3 sleep) and REM sleep had smaller volumes in a key brain region that typically shows early Alzheimer’s changes [2]. Specifically, insufficient deep and REM sleep was associated with shrinkage of the inferior parietal lobule, an area involved in integrating sensory and spatial information and one of the first regions to deteriorate in Alzheimer’s disease [2]. Dr. Gawon Cho, the study’s lead author, noted this provides "preliminary evidence that reduced neuroactivity during sleep may contribute to brain atrophy, thereby potentially increasing the risk of Alzheimer’s disease" [2]. Interestingly, slow-wave sleep and REM sleep serve to clear out weak memories and strengthen strong memories, respectively [9,10].  In other words, not getting enough of these sleep stages could be setting the stage for memory loss and neurodegeneration later in life.

This new finding adds to a growing body of research showing that quality sleep – particularly deep slow-wave sleep and REM dream sleep – is critical for long-term brain health. From solidifying our memories to clearing out cellular waste, these stages of sleep perform vital "housekeeping" for the brain. Here, we delve into what recent science (2022–2025) is revealing about how deep sleep keeps our brains sharp, balanced, and protected as we age.

Deep Sleep and Memory: Reinforcing What We Learn

One of the best-established roles of sleep is in memory consolidation – the process by which new experiences and information are transformed into lasting memories. Deep slow-wave sleep (SWS) plays a starring role in this nightly memory workshop. During healthy N3 deep sleep, neurons in the hippocampus (a memory center) repeatedly replay patterns of activity from recent experiences, while the cortex simultaneously generates synchronized slow brain waves and brief bursts called sleep spindles [3]. In contrast, these slow-waves coupled to spindles are reduced in Alzheimer’s disease [11] and possibly account for memory loss.  

In healthy brains, this coordinated brain activity effectively "rehearses" and transfers new memories from short-term storage in the hippocampus to long-term storage in the cortex. Recent studies have provided direct evidence for this replay mechanism. For example, neuroscientists in 2023 showed that boosting the natural synchronized oscillations between the hippocampus and frontal cortex during deep sleep can improve recall of learned information [3].

Such findings reinforce decades of research showing that a night of solid deep sleep greatly strengthens our ability to remember facts and events. On the flip side, when deep sleep is disrupted or shortened, memory suffers. A 2022 review of sleep and memory concluded that sleep deprivation (especially loss of SWS) impairs the hippocampus’s ability to encode new memories, leaving us more forgetful and less able to learn the next day [4]. In short, deep sleep is when the brain files away our daily learning – without it, those files remain messy or never properly saved. By securing memories overnight, healthy deep sleep in midlife may also help preserve cognitive function long-term, creating a more resilient brain as we age.

Sweeping Out Toxins: The Brain’s Nightly Cleanup

Beyond cementing memories, deep sleep literally cleans the brain. During slow-wave sleep, the brain undergoes a remarkable housekeeping process to flush out metabolic waste and neurotoxic byproducts that build up during the day. Neuroscientists have discovered a brain-wide "glymphatic system" – a network of channels in the brain tissue – that pumps cerebrospinal fluid through the brain to wash away debris like misfolded proteins.

Crucially, this glymphatic cleansing is most active during deep N3 sleep. In fact, time spent in slow-wave sleep has been shown to correlate with greater clearance of waste metabolites and toxic protein fragments from the brain [5]. One landmark study demonstrated that during deep sleep, brain cells actually shrink slightly, expanding the spaces between cells so that fluid can flow through and carry away toxins such as beta-amyloid (the protein that aggregates in Alzheimer’s) [5].

Think of deep sleep as the brain’s nighttime janitorial staff: cerebral fluid washes through the brain, clearing out "trash" – including compounds linked to neurodegeneration. Without adequate deep sleep, these garbage-removal processes slow down. Over years, poor sleep could allow amyloid and other toxins to accumulate, contributing to memory loss and dementia risk. Encouragingly, emerging research suggests that improving slow-wave sleep might enhance glymphatic flow. Animal studies in 2022, for instance, found that stimulating deep-sleep brain waves led to increased clearance of waste in the brain [5]. While scientists are still untangling all the details of the brain’s cleaning system, the message is clear: deep sleep is likely a critical neuroprotective force, giving the brain a chance to wash away harmful build-up each night.

REM Sleep: Emotional Processing and Mental Health

What about REM sleep, the stage when most vivid dreaming occurs? REM has long been thought to play a key role in processing emotions and maintaining mental health. During REM sleep, the brain is highly active – consolidating memories with emotional tone, integrating experiences, and possibly dampening the sting of painful memories. If you’ve ever "slept on it" and felt less upset the next day, you can thank the therapeutic effect of REM sleep.

Recent research continues to uncover REM’s influence on emotional regulation. For example, a 2023 study on sleep apnea patients (who often have fragmented REM sleep) found that those with chronically reduced REM showed worse emotional memory and signs of mood dysregulation, compared to people with normal REM-rich sleep [6]. In healthy adults, scientists have observed that depriving someone specifically of REM sleep night after night can lead to heightened anxiety, irritability, and difficulty managing stress [6].

In contrast, sufficient REM sleep appears to "reset" the brain’s emotional circuits. During REM, the stress neurotransmitters noradrenaline and serotonin are modulated, and the amygdala (the fear center) replays emotional experiences in a neurochemical milieu that softens their impact. This may be why we often gain emotional clarity after a good night’s sleep – REM sleep helps us process and cope with yesterday’s emotions. Studies have even shown that after REM-rich sleep, people’s emotional reactions are more balanced and measured, whereas lack of REM causes a spike in reactivity (the brain’s alarm centers go into overdrive) [6].

Sleep Loss, Brain Aging, and Neurodegeneration

Deep and REM sleep aren’t just important in the moment – they accumulate into long-term brain benefits. Conversely, years of sleep deficiency can accelerate aspects of brain aging and increase the risk of neurodegenerative diseases like Alzheimer’s. The recent Yale study covered by CNN is a striking example: it suggests that even in midlife, people who routinely skimp on deep/REM sleep show early signs of brain atrophy [2].

In fact, a 2024 study in the journal Neurology found that 40-year-olds who had multiple chronic sleep problems (such as short sleep, poor quality, and frequent awakenings) had brains that appeared 1.6 to 2.6 years older by their mid-50s, based on MRI scans [7]. That is, poor sleepers in midlife showed more brain shrinkage and aging-related changes than those who slept well – a difference measured in years of "brain age." Importantly, the worst outcomes were seen in those with persistently broken sleep over time [7].

The connection to Alzheimer’s disease is especially concerning. Alzheimer’s involves an accumulation of amyloid plaques and tau tangles in the brain, processes that are thought to be exacerbated by chronic sleep deprivation. Longitudinal research has shown that people in their 50s and 60s who consistently sleep less than ~6 hours per night have a significantly higher risk of developing dementia decades later [8].

Scientists believe that lack of deep sleep allows more amyloid to collect (since the brain isn’t cleaning itself as effectively), which can kick off a cascade of neurodegeneration [5]. There is also evidence that as Alzheimer’s pathology silently begins in the brain, it further disrupts sleep – creating a vicious cycle where poor sleep and disease progression feed into each other. However, the hopeful flip side is that sleep might be a modifiable risk factor. The Yale researchers pointed out that sleep quality (how much time we spend in each stage) could be improved as a preventive strategy [2].

If boosting deep and REM sleep can be shown to slow down cognitive decline or delay Alzheimer’s onset, it would be a game-changer for public health. Indeed, neurologists are now asking whether interventions like sleep coaching, acoustic stimulation during deep sleep, or treating sleep disorders aggressively in midlife could add healthy years to our brains.

Elemind: Harnessing Science for Sleep 

The growing recognition that "sleep is brain care" has spurred interest in new technologies to improve sleep quality. Elemind is at the forefront of this movement, developing a science-driven, non-invasive way to help people optimize sleep.

Our team at Elemind – comprised of neuroscientists and sleep experts – understands that true sleep enhancement must work with the brain’s natural rhythms. That’s why we designed the Elemind headband to gently guide your brain into sleep, and down the road, enhance deep sleep,  through real-time brainwave monitoring and personalized acoustic stimulation. Elemind’s technology reads your brain’s attention-related alpha oscillations using electrical activity (EEG) as you drift off and sleep, and emits precisely timed gentle sound pulses to modulate the attention-related brainwaves and to nudge the brain toward the slower wave patterns of sleep. 

This closed-loop system effectively coaxes the brain out of wake-like activity and into the slower, synchronized waves of N3 deep sleep, all while you peacefully slumber. Importantly, it’s completely non-invasive – using sound rather than any drugs – and is calibrated to work invisibly with your natural sleep cycles. Our goal is to elevate the quality and performance of sleep for users: helping you fall asleep faster, ultimately spend more time in deep and REM stages, and wake up feeling mentally sharp and refreshed.

We envision a future in which enhancing one’s sleep isn’t a shot in the dark, but a precise, personalized process backed by neuroscience – as easy as wearing a comfortable headband at night. 

With society facing rising rates of burnout, memory issues, and neurodegenerative illness, prioritizing sleep has never been more crucial. The latest science makes it abundantly clear: sleep is one of the best investments you can make in your long-term brain health. Elemind is excited to help you make that investment, unlocking the power of your own brain to heal, cleanse, and fortify itself each night – so you can thrive each day and for years to come.

References:

1. LaMotte, S. (2025). “Alzheimer’s risk rises when amount of deep sleep falls, study suggests.” CNN Health, March 30, 2025.  https://www.cnn.com/2025/03/31/health/deep-rem-sleep-alzheimers-wellness/index.html
   
2. American Academy of Sleep Medicine (AASM). “New study links lower proportions of certain sleep stages to brain changes associated with Alzheimer’s disease.” ScienceDaily, March 31, 2025.  https://aasm.org/study-sleep-stages-brain-changes-alzheimers-disease/
   
3. Brodt, S., Inostroza, M., Niethard, N., & Born, J. (2023). “Sleep — a brain-state serving systems memory consolidation.” Neuron, 111(7), 1050-1075.  https://pubmed.ncbi.nlm.nih.gov/37023710/
   
4. Rawson, G., & Jackson, M. L. (2024). “Sleep and Emotional Memory: A Review of Current Findings and Application to a Clinical Population.” Current Sleep Medicine Reports, 10(4), 378–385.  https://link.springer.com/article/10.1007/s40675-024-00306-8
   
5. Pathmanathan, J., & Westover, M. B. (2025). “The role of sleep in Alzheimer’s disease: a mini review.” Frontiers in Neuroscience, in press. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2025.1428733/full
   
6. Jackson, M. L. et al. (2023). “REM sleep and emotional reactivity: Current findings and future directions.” Sleep Medicine Reviews.
   
7. Cavailles, C., et al. (2024). “Association of self-reported sleep characteristics with neuroimaging markers of brain aging years later in middle-aged adults.” Neurology, published online Oct 23, 2024.  https://www.neurology.org/doi/10.1212/WNL.0000000000209988
   
8. Sabia, S., et al. (2021). “Association of sleep duration in middle age with incident dementia.” Nature Communications, 12:2289. https://www.nature.com/articles/s41467-021-22354-2
   
9. González-Rueda A, Pedrosa V, Feord RC, Clopath C, Paulsen O. Activity-Dependent Downscaling of Subthreshold Synaptic Inputs during Slow-Wave-Sleep-like Activity In Vivo. Neuron. 2018 Mar 21;97(6):1244-1252.e5. doi: 10.1016/j.neuron.2018.01.047. Epub 2018 Mar 1. PMID: 29503184; PMCID: PMC5873548.
   
10. Li W, Ma L, Yang G, Gan WB. REM sleep selectively prunes and maintains new synapses in development and learning. Nat Neurosci. 2017 Mar;20(3):427-437. doi: 10.1038/nn.4479. Epub 2017 Jan 16. PMID: 28092659; PMCID: PMC5535798.
    
11. De Gennaro L, Gorgoni M, Reda F, Lauri G, Truglia I, Cordone S, Scarpelli S, Mangiaruga A, D'atri A, Lacidogna G, Ferrara M, Marra C, Rossini PM. The Fall of Sleep K-Complex in Alzheimer Disease. Sci Rep. 2017 Jan 3;7:39688. doi: 10.1038/srep39688. PMID: 28045040; PMCID: PMC5206737.