Many of us are familiar with the rapid eye movement phases of sleep, when slumbering people\u2019s eyes flicker back and forth under their lids and most dreaming occurs. But non-REM sleep \u2014 a deeper form of sleep with little, if any, dreaming \u2014 is crucial for brain health.\u00a0<\/p>\n
During non-REM sleep, neurons shut down in slow, synchronized waves that move across the brain, beginning in the frontal cortex.\u00a0<\/p>\n
This coordinated shutdown has been observed only during deep sleep, and may be one reason why we sleep.<\/p>\n
Omer Sharon, UC Berkeley Postdoctoral Researcher<\/p>\n
\u201cEach slow wave reflects an enormous population of neurons switching off and back on together,\u201d Sharon said. \u201cOur study shows that for memory, it\u2019s critical that these events cascade in sequence across large parts of the brain. This coordinated shutdown has been observed only during deep sleep, and may be one reason why we sleep.\u201d<\/p>\n
As we age, tau proteins build up in many people\u2019s brains. For them, these waves become irregular and less synchronized and travel shorter distances. This slow-wave breakdown is in turn linked to dwindling memory consolidation, cognitive decline and the development of Alzheimer\u2019s disease.\u00a0<\/p>\n
To study this correlation, the researchers used electroencephalograms (EEGs) to measure brain waves during sleep. They compared results from cognitively healthy participants in their early 20s to those from their mid-60s to mid-70s. In the younger adults, clusters of slow brain waves traveled roughly the length of a handspan across the scalp during non-REM sleep. In the older adults, the waves traveled shorter distances and were more solitary.\u00a0<\/p>\n
Using positron emission tomography (PET) scans conducted with Dr. William Jagust, a professor emeritus in public health and neuroscience at Berkeley, the researchers traced\u00a0 radioactive markers injected into the bloodstream to measure brain function. The scans confirmed that the buildup of tau in the frontal cortex of older participants correlated with those long wave breakdowns.\u00a0<\/p>\n
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In healthy older study participants, PET scans revealed the protein tau building up over time in their frontal cortices. This buildup correlates with shortened, isolated slow brain waves during sleep and with memory loss.<\/p>\n
Courtesy of Omer Sharon\/UC Berkeley Department of Psychology<\/p>\n
This interference with slow brain waves shows up even before patients develop Alzheimer\u2019s disease. \u201cThese people did not have Alzheimer\u2019s,\u201d Sharon said. \u201cThey had tau in their brains, but with subclinical impacts. Their memory decline was within the normal range for their age.\u201d Indeed, Alzheimer\u2019s symptoms appear along a spectrum at first, Sharon said, with the amount of tau in a person\u2019s brain correlating to cognitive performance.<\/p>\n
The researchers also measured corresponding changes in memory consolidation by giving participants word associations at night, then testing how well they remembered them the next day. People with more solitary, shorter-reaching slow waves \u2014 what the researchers called \u201clonely waves\u201d \u2014 remembered less material.<\/p>\n
After several years, a subset of participants was retested. Those whose frontal tau had increased over the years had worsened slow-wave coordination and lessened overnight memory retention. While this does not prove that frontal cortex tau buildup causes memory loss, it indicates that there is a connection between the protein and episodic memory loss that is related in some way to brain wave changes.\u00a0<\/p>\n
PET scans are expensive and require specialized equipment, making them hard to arrange, so the researchers worked with neurologist Yo-El Ju at Washington University in St. Louis to measure tau levels in the spinal fluid of a different group of elderly people. Although this test didn\u2019t reveal tau buildup specifically in the frontal cortex, a similar pattern emerged: The spinal fluid from participants whose brains had more solitary slow waves during sleep contained higher ratios of tau to another Alzheimer\u2019s disease linked protein, amyloid.<\/p>\n
Sharon found it convincing to see these different methods arrive at converging results. \u201cIt\u2019s collected in a totally different place and in a different cohort, so I think that adds to the strength of the evidence,\u201d he said.<\/p>\n
Altogether, the multiple measures led the researchers to connect tau buildup, a known form of Alzheimer\u2019s pathology, with a specific kind of brain function. \u201cThis longitudinal correlation suggests that Alzheimer\u2019s disease pathology is associated with a disruption of this main sleep feature,\u201d Sharon said.\u00a0<\/p>\n
And though it remains unclear to researchers why memory loss is correlated with aging, the findings suggest that the connection is more complex than previously thought. \u201cIt\u2019s not just about age,\u201d Sharon said. \u201cIt\u2019s how much pathology you have in frontal areas where global waves originate.\u201d It\u2019s also about sleep quality \u2014 a hard-to-define concept for which slow waves seem to be proxies.\u00a0<\/p>\n
\u201cWe can see tau and lonely waves rising together over time,\u201d Sharon said. \u201cWhat we cannot yet say is which leads \u2014 and that question will shape how we design interventions.\u201d\u00a0<\/p>\n
Other co-authors of the study include Xi Chen, James Westphal, Chelsea Brown and Vyoma D. Shah at UC Berkeley, and Jason Dude at Washington University in St. Louis.<\/p>\n
This research was supported by grants from the National Institute on Aging at the National Institutes of Health. Sharon was supported by a Glenn Foundation for Medical Research Postdoctoral Fellowship and a Weil Neurohub Fellowship.<\/p>\n","protected":false},"excerpt":{"rendered":"You\u2019re hurrying out of the grocery story to drive home and start cooking dinner. As the doors close…\n","protected":false},"author":2,"featured_media":460502,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[34],"tags":[1570,87009,143,145,144,8939],"class_list":["post-460501","post","type-post","status-publish","format-standard","has-post-thumbnail","category-oakland","tag-health","tag-neuroscience","tag-oakland","tag-oakland-headlines","tag-oakland-news","tag-press-releases"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts\/460501","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/comments?post=460501"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/posts\/460501\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/media\/460502"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/media?parent=460501"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/categories?post=460501"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us-ca\/wp-json\/wp\/v2\/tags?post=460501"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}