Sleep

How sleep acts on the brain

Eating fish linked to better sleep and higher I.Q. for kids

A largish Chinese study, involving 541 9-11-year-olds, has found that those who ate fish at least once a week slept better and had higher IQ scores, on average, than those who ate fish less frequently or not at all.

The study suggests that sleep may be a reason for the association previous research has found between the consumption of fish / omega-3 oils and better cognition.

Children who reported eating fish weekly scored 4.8 points higher on the IQ tests than those who said they “seldom” or “never” consumed fish. Those whose meals sometimes included fish scored 3.3 points higher.

Reference: 

Liu, J., Cui, Y., Li, L., Wu, L., Hanlon, A., Pinto-Martin, J., Raine, A., & Hibbeln, J. R. (2017). The mediating role of sleep in the fish consumption – cognitive functioning relationship: A cohort study. Scientific Reports, 7(1), 17961. https://doi.org/10.1038/s41598-017-17520-w

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Memory consolidation during sleep depends on coordinated brain activity

  • New research shows memory consolidation requires simultaneous replay with hippocampal 'ripples'. These may depend on deeper processing.

A study involving epilepsy patients who had electrodes implanted into their brain has revealed that memory consolidation during sleep doesn’t simply involve reactivation of the new memories.

Participants were given pictures to memorize, before taking an afternoon nap. Surprisingly, brainwave activity showed that both the pictures participants later remembered and those they later forgot, were reactivated during sleep. What was crucial was not the reactivation of the picture-specific gamma band activity, but its conjunction with “ripples” (extremely rapid fluctuations in activity) in the hippocampus. Only when the reactivation occurred at the same time as the ripples in the hippocampus did participants remember the picture.

What determined whether this happened? The evidence suggests that longer (and thus deeper) processing of the picture is needed, not simply a quick superficial look.

This phenomenon only occurred during nonREM sleep, not during wakefulness (the circumstances of sleep meant little time was spent in REM sleep).

The findings confirm earlier research with rodents.

https://www.eurekalert.org/pub_releases/2018-10/rb-htb100518.php

Paper available at https://www.nature.com/articles/s41467-018-06553-y

Reference: 

[4394] Zhang, H., Fell J., & Axmacher N.
(2018).  Electrophysiological mechanisms of human memory consolidation.
Nature Communications. 9(1), 4103.

 

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Sleep helps process traumatic experiences

  • A finding that sleeping after watching a trauma event reduced emotional distress and traumatic memories is intriguing in light of the theory that PTSD occurs through a failure of contextual processing.

A laboratory study has found that sleeping after watching a trauma event reduced emotional distress and memories related to traumatic events. The laboratory study involved 65 women being shown a neutral and a traumatic video. Typically, recurring memories of certain images haunted the test subjects for a few days (these were recorded in detail in a diary). Some participants slept in the lab for a night after the video, while the other group remained awake.

Those who slept after the film had fewer and less distressing recurring emotional memories than those who were awake. This effect was particularly evident after several days.

 One of the reasons for this benefit is thought to be that the memory consolidation processes that happen during sleep help contextualize the memories. This is interesting in view of the recent theory that PTSD is associated with a deficit in contextual processing.

However, I'd note that there is conflicting evidence about the effects of sleep on negative memories (for example, see http://www.memory-key.com/research/news/sleep-preserves-your-feelings-about-traumatic-events).

https://www.eurekalert.org/pub_releases/2016-12/uoz-shp121316.php

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Sleep helps you remember new names

  • A small study has found that a night's sleep helps you better remember new names.

Sleep, as I have said on many occasions, helps your brain consolidate new memories. I have reported before on a number of studies showing how sleep helps the learning of various types of new information. Most of those studies have looked at procedural learning (learning new skills), or verbal learning. A new study adds to these by looking at face-name associations.

The small study, involving 14 young adults, found that that they were significantly better at remembering faces and names if they were given an opportunity to have a full night's sleep hours after seeing those faces and names for the first time.

Participants were shown 20 photos of faces with corresponding names and asked to memorize them. After a twelve-hour period, they were then shown the photos again with either a correct or incorrect name. They were also asked to rate their confidence in their answer. Each participant completed the test twice — once with an interval of sleep in between and once with a period of regular, waking day activities in between.

After a night's sleep, participants correctly matched 12% more of the faces and names, and were much more confident of their answers.

Of course, this is not a huge difference, given the small number of face-name pairs, and the sample is small. I would have also liked to see further testing 12 hours later, so that we could compare the effects of a day followed by a night, versus a night followed by a day (this would have required more stimuli and more participants, of course).

So, not madly exciting, but taken in context of other research, it adds to the growing evidence that sleep helps you consolidate new learning of all kinds.

http://www.eurekalert.org/pub_releases/2015-11/bawh-wtr112315.php

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Sleeping on your side best for clearing waste from brain

  • Waste products accumulate as the brain functions.
  • The process of clearing this waste is most effective during sleep.
  • Accumulation of waste products such as amyloid-beta and tau proteins are involved in Alzheimer's.
  • Rat study shows sleeping on your side is best for removing waste from the brain.

This sounds like pseudoscience, but it appears in Journal of Neuroscience, so … Weirdly, a rat study has found that sleeping on the side (the most common posture for humans and other animals) is the best position for efficiently removing waste from the brain.

Brain waste includes amyloid-beta and tau proteins, whose build-up is a critical factor in the development of Alzheimer's disease.

The study used imaging of the glymphatic pathway, which clears waste products from the brain by filtering cerebrospinal fluid through the brain and exchanging it with interstitial fluid. The process is most efficient during sleep, and its efficiency is affected by the level of consciousness. The researchers compared glymphatic transport during sleep when anesthetized rodents’ brains were in three positions—lateral (side), prone (down), and supine (up).

Of course, these findings need to be confirmed in humans (which might be tricky!), but there is, after all, no harm in changing your sleep position, if you don't already sleep on your side (though I concede it can be a difficult thing to change).

Apart from providing a practical tip for fighting age-related cognitive decline and dementia, the finding also supports the idea that one of the purposes of sleep is to ‘clean up’ the mess that accumulates while we are awake.

The finding is also consistent with increasing evidence that sleep disturbances are a factor in the development and progression of dementia.

http://www.futurity.org/side-sleeping-brains-979872/

Reference: 

[3956] Lee, H., Xie L., Yu M., Kang H., Feng T., Deane R., et al.
(2015).  The Effect of Body Posture on Brain Glymphatic Transport.
The Journal of Neuroscience. 35(31), 11034 - 11044.

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Reactivate if you want to remember

We know sleep helps consolidate memories. Now a new study sheds light on how your sleeping brain decides what’s worth keeping. The study found that when the information that makes up a memory has a high value—associated with, for example, making more money—the memory is more likely to be rehearsed and consolidated during sleep.

05/2013

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