New Study Finds Sleep Apnea May Cause Damage to Brain Areas That Support Memory
A new study published in the journal Neurology has found that obstructive sleep apnea — a common sleep disorder that lowers oxygen levels during rest — is associated with damage to brain regions crucial for memory. The research shows that lower oxygen saturation during rapid eye movement (REM) sleep correlates with structural changes in the brain, particularly in areas such as the hippocampus and entorhinal cortex, both essential for storing and retrieving memories. These changes are also linked to poorer memory performance, providing new insight into how sleep disorders may contribute to age-related cognitive decline and potentially even Alzheimer’s disease.
How the Study Linked Sleep Apnea to Memory-Related Brain Changes
According to Neuroscience News, the study was led by neuroscientist Bryce A. Mander, PhD, from the University of California, Irvine, in collaboration with colleagues from the UCI Center for the Neurobiology of Learning and Memory. The research was published online on May 7, 2025, in Neurology (https://doi.org/10.1212/WNL.0000000000213639), the medical journal of the American Academy of Neurology, one of the most reputable journals in the field of brain health.
The study included 37 older adults (average age 73) with no diagnosed cognitive impairments and who were not taking sleep medications. Of these, 24 participants had obstructive sleep apnea (OSA), while the rest served as control subjects.
Researchers conducted overnight sleep studies on all participants to monitor oxygen levels during all stages of sleep, focusing particularly on REM sleep, the phase known for its role in memory consolidation and emotional processing.
Participants also underwent high-resolution brain imaging (MRI) to detect structural brain changes and took memory tests before and after sleep to assess how well memory was formed or retained overnight — a concept known as sleep-dependent memory.
What Makes This Study Different?
Previous research had already shown that obstructive sleep apnea can affect cognitive function, but the mechanisms were not well understood. This study is innovative in several ways:
- Focus on REM sleep, not just sleep overall.
- Measurement of white matter hyperintensities — specific signs of small vessel disease — as a biological marker of damage.
- Detailed imaging of brain regions involved in memory, including the hippocampus and entorhinal cortex.
- Use of sleep-dependent memory tests, offering a behavioral link to structural brain changes.
Unlike earlier studies that measured general sleep quality or total oxygen levels, this research highlights the critical role of oxygen saturation during specific sleep stages — especially REM — in affecting brain health.
Key Findings of the Study
1. Low Oxygen During REM Sleep Harms Small Blood Vessels in the Brain
Participants with lower oxygen levels during REM sleep had higher levels of white matter hyperintensities, which appear as bright spots on brain scans. These are signs of small vessel damage, which can silently progress without symptoms for years.
Example: Imagine a 73-year-old individual who snores loudly and feels tired during the day. This study suggests that if their REM sleep is frequently interrupted by drops in oxygen, their brain may be slowly accumulating microvascular damage.
2. Memory Centers of the Brain Show Signs of Atrophy
The study found that this vessel damage was associated with shrinkage in the hippocampus and thinning of the entorhinal cortex — two brain areas essential for forming and recalling memories.
Example: A person with untreated sleep apnea might experience mild forgetfulness or trouble recalling names — symptoms often dismissed as normal aging — but could actually be showing early signs of brain atrophy.
3. Poorer Memory Performance After Sleep
Participants with more brain changes also performed worse on memory tests taken after sleep, suggesting a direct link between the structural changes and real-world cognitive function.
Example: A retiree might notice that they forget the details of a conversation from the previous day or misplace items more frequently. The study implies these problems could be tied to poor-quality REM sleep due to apnea.
4. The Degree of Brain Damage Correlates with Severity of Oxygen Drops
Researchers found that not only did minimum blood oxygen levels matter, but also the total time spent with oxygen below 90% during sleep predicted the amount of brain damage observed.
Example: People who spend even short periods at night with oxygen levels dipping below the healthy range may be at greater risk of cognitive decline, even if they feel fine during the day.
5. Damage Likely Builds Up Over Time
The study focused on older adults with no diagnosed dementia, suggesting that these changes begin before clinical symptoms appear. This adds to the evidence that early detection and treatment of OSA may be key to preventing future decline.
Example: An older adult newly diagnosed with sleep apnea may benefit not just from feeling more rested but also from protecting long-term brain health by starting treatment early.
How Sleep Apnea May Undermine Memory and Learning Over Time
The study provides strong biological evidence that obstructive sleep apnea affects not just sleep quality, but also the brain’s ability to process and store information. The most critical stage affected is REM sleep, which plays a key role in consolidating new memories, processing emotions, and integrating learning experiences from the day.
Researchers found that lower oxygen levels during REM sleep were linked to structural changes in two brain regions — the hippocampus and entorhinal cortex — that are essential for forming, storing, and retrieving memories. When these areas are damaged, the brain becomes less efficient at handling both short-term and long-term memory functions.
Moreover, the study found that damage to these memory-related areas was directly associated with poorer sleep-dependent memory performance. That means the brain was less able to retain information learned before sleep and struggled more with recalling it the next day — a process that healthy REM sleep typically supports.
These findings suggest that cognitive abilities such as recall, learning, problem-solving, and even emotional regulation may all be gradually weakened in individuals with untreated sleep apnea. While these deficits might appear subtle at first, over time they could contribute to noticeable cognitive decline and possibly increase the risk of conditions like mild cognitive impairment or Alzheimer’s disease.
Why These Findings Matter for Brain Health and Everyday Life
This research highlights how a common and often overlooked sleep disorder may have direct consequences for brain structure and memory. By showing that lower oxygen levels during REM sleep are linked to damage in key memory regions, the study helps explain why some people with sleep apnea experience cognitive issues over time.
From a scientific perspective, the findings clarify how disrupted sleep can lead to physical changes in the brain. Previous research had hinted at a connection between sleep apnea and memory decline, but this study provides visual and measurable evidence of changes in the hippocampus and entorhinal cortex — areas essential for learning and recall.
For healthcare professionals, the study adds weight to the idea that sleep disorders should be considered when patients report forgetfulness or difficulty concentrating. The structural changes observed on brain scans may begin long before obvious symptoms appear, making early identification and treatment of sleep apnea even more important.
On a personal level, the results are a reminder that good sleep is not just about feeling rested — it’s also about protecting long-term brain function. Many people may not realize that nighttime breathing disruptions can gradually affect their ability to remember, learn new things, or stay mentally sharp with age.
In short, the study underscores how sleep health and brain health are closely linked. Managing conditions like obstructive sleep apnea may be one of the practical ways to support memory and mental clarity as we grow older.
Final Thoughts
The study provides clear evidence that sleep apnea, particularly when it affects oxygen levels during REM sleep, may contribute to measurable changes in brain regions responsible for memory. While the research does not establish a direct cause-and-effect relationship, the associations between reduced oxygen saturation, small vessel damage, and memory-related brain atrophy are consistent and well documented.
These findings reinforce the importance of recognizing and managing sleep apnea not only for general well-being, but also as part of a broader strategy to support cognitive health with age. Addressing sleep-related breathing issues early may help reduce the risk of memory impairment and structural brain changes over time.
Understanding the link between sleep quality and brain structure highlights the role of sleep in maintaining memory, learning capacity, and mental clarity — all of which are essential for healthy aging.
