Sleepy? Your memory may be impaired

Everyone has had one of those days where a night of choppy or short sleep leads into a morning of mental haze. New research presented at the Neuroscience 2012 conference suggests that sleep deprivation might be worse for you than you think.

For starters, sleepiness in the elderly could be an indication of Alzheimer's risk, says Andrew Ward, researcher at Massachusetts General Hospital.
Ward and colleagues did a study involving 84 elderly adults without memory problems, ranging from age 66 to 87. Researchers gave them a questionnaire about how likely they were to fall asleep during various daily activities, as a way to measure sleepiness. They also measured brain activity using functional magnetic resonance imaging (fMRI).

Researchers found that the sleepy study participants tended to show less coordinated activity in the default mode network, brain regions that are active when the brain is resting and are involved in introspection.
This suggests that people with bad sleep may be more susceptible to Alzheimer’s, but "we need to do more research to see if this is actually true," Ward said. The next step would be to follow the participants over time to see who develops Alzheimer's in the long term. The study also suggests that improvements in sleep may restore network connectivity - but again, further investigation is necessary to make more substantial conclusions.
Elderly people generally sleep fewer hours and wake up more frequently during the night than their younger counterparts, Ward said. And reports from Alzheimer's caregivers suggest that people with worse sleep have more severe memory impairments.
A second study also emphasized the importance of getting a good night's sleep. Hengi Rao, a researcher at the University of Pennsylvania, presented an experiment involving sleep deprivation in a laboratory. Participants spent four nights in the lab as researchers controlled their number of sleeping hours, gave them memory tests and scanned their brains (doesn't that sound fun!).
The 22 healthy adults slept nine hours the first night, went 24 hours without sleeping, and then spent two nights gaining recovery sleep. Their brains were scanned after nights 1, 2 and 4.
After sleep deprivation, researchers found that participants showed less connectivity between the default mode network and the hippocampus, a region of the brain essential for memory. After recovery sleep, however, their brains showed the same activity as after that first night of nine hours of sleep. Their performance on memory tasks was correlated to the activity in these regions.
"It’s critical to obtain recovery sleep after sleep loss and avoid chronic sleep deprivation" in order for the brain to restore the integrity of this neural network, Rao said.
How much sleep loss are we talking about? Ted Abel of the University of Pennsylvania discussed a study he's involved with using mice. Of course, mice are not perfect approximations for humans, but may give some insight into what's going on in the human body. It turns out that mice show memory impairment after being deprived only about three hours of their normal sleep, which translates into 20% of their daily total.
If animal models are to be believed, memory strengthening can be affected in a human who sleeps six hours instead of eight hours, this study suggests.
Bottom line: Getting a good night's sleep is important for memory.
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