Snore a lot? Get up frequently at
night to urinate? Wake up at 2 A.M. with bright ideas or worries? All these
disruptions of sleep are common and more so as we get older. Does it matter?
Well, of course such awakenings disrupt our sleep, and maybe it is just
inconvenient. But disrupted sleep not only is more likely with age, it may
promote deterioration in mental functioning. A recent study compared the
effects of sleeping behavior in young adults and seniors. The study involved
assessing the memory after sleeping of 18 young adults in their 20s and 15
older adults in their 70s. The subjects were tested on 120 word sets before
they went to bed, and an EEG machine monitored their brain activity while they
slept. Upon awakening, they were tested once again on the word pairs, but this
time they took the tests while undergoing functional magnetic resonance imaging (fMRI) scans.
The quality of deep sleep among the older adults was 75 percent lower
than the younger ones, and their memory was significantly worse the next day−55
percent worse. The scans suggested deterioration of the frontal
lobe. Shrunken brains can occur from aging and shrunken brains impair
thinking and memory. But is it possible we have the cause and the effect
backwards. Maybe what happens in the environment, such as impaired sleeping,
causes both the shrunken brain and the impaired memory. Or in other words, what
causes older brains to shrink?
Scientists consider a decrease of
about 2% shrinkage every 10 years as normal. That may not be normal, just what
most people experience because they are not taking care of their brains. There
is abundant research that shows that exercises for both the brain and body help
to reduce brain atrophy.
Of course, anything that damages
neurons can reduce the number of their tree-like processes and the density of
their contact points with other neurons. The list of such causes is long,
including: alcohol abuse, brain inflammation, certain infections, concussion,
impaired blood supply, lack of intellectual stimulus, vitamin B12 deficiency. It
now appears that we should add fragmented sleep to the list.
Common natural causes of
fragmented sleep in older humans are alcohol abuse and sleep apnea. Also, in
males, enlarged prostate causes a need for frequent urination. As I have
explained in my learning and memory blog posts (thankyoubrain.blogspot.com),
learning events during the day are consolidated into lasting form during the
sleep at night of the same day. We don’t know exactly how sleep helps, but
obviously, you have far fewer mental distractions during sleep — unless, of
course you keep waking up.
Alzheimer’s Disease also causes
fragmented sleep. So, it is no surprise that the brain degeneration by the
disease would cause memory problems. But maybe, just maybe, it is the
fragmented sleep that accelerates onset of Alzheimer’s disease. Now, this
seemingly ridiculous possibility has to be taken seriously in light of new
research showing that sleep-disordered breathing, as in sleep apnea, seems to
increase the risk of mental decline and even dementia in older women.
Disrupted sleep may also
accelerate normal aging. This is certainly true when the cause is sleep apnea,
which raises blood pressure and increases the cardiovascular damage that high
blood pressure causes. Blood clotting is promoted, increasing the likelihood of
strokes. Obesity and diabetes are often associated with sleep apnea, and it
seems that sleep apnea not only results from obesity but can promote obesity
and the diabetes that often accompanies obesity. Diabetes is toxic for nerve
terminals. Similar neuropathy may also be occurring in their brain. Sleep apnea
causes daytime sleepiness, and that it turn reduces attentiveness and mental
activity, which when sustained over many years reduces the mental stimulus and
promotes atrophy of neuronal processes.
Obviously, blood oxygen drops
during sleep apnea. Normally, blood is 94% to 98% saturated with oxygen. But
not breathing for 30 seconds or more during sleep causes oxygen level to drop
to 80% or less. Any level below 90% oxygen level is dangerous, especially to
the brain which demands nearly 20% of all the body’s oxygen supply. The adult
brain can only survive about four minutes once oxygen is completely cut off.
So it is entirely possible that
the slipping memory we see in so many elderly is a warning sign of something
much more serious. But by the time the memory deficits show up, much of the
damage has already been done. Prevention is the best hope.
Source:
Mander, B. A., Rao, V.,
Brandon, B. L., Saletin, J. M., et al. (2013). Prefrontal atrophy,
disrupted NREM slow waves and impaired hippocampal-dependent memory in aging. Nature
Neuroscience doi:10.1038/nn.3324
Yaffe, K., Laffan, A. M., Harrison, S. L. et al. (2011).
Sleep-disordered breathing, hyupoxia, and risk of mild cognitive impairment and
dementia in older women. JAMA. 306
(6), 613-619. doi:10.1001/jama.2011.1115
Lack of sleep is always causes depression and so many brain diseases. You elaborated comprehensively the effects of lack of sleep. I appreciate your work and thank you so much for such informative topic. traumatic brain injury
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