“After a good night's sleep, people remember information better when they know it will be useful in the future, according to a new study in the Feb. 2 issue of The Journal of Neuroscience. The findings suggest that the brain evaluates memories during sleep and preferentially retains the ones that are most relevant.”

http://www.eurekalert.org/pub_releases/2...012811.php

Original paper's not online yet; till then I'll have to wonder how they eliminated consideration of the waking time between informing them and taking the test.

Well. I hope they bring it up in the original paper but there seems like there could be quite a lot of interference from exhaustion effects...

"In both groups, half the volunteers were told immediately following the tasks that they would be tested in 10 hours. In fact, all participants were later tested on how well they recalled their tasks.

Some, but not all, of the volunteers were allowed to sleep between the time they learned the tasks and the tests. As the authors expected, the people who slept performed better than those who didn't. But more importantly, only the people who slept and knew a test was coming had substantially improved memory recall. "

Ten hours awake means that, optimally, the ones who weren't allowed to sleep did the test in the morning and then a second time in the late afternoon. Since most of us tend to perform poorly when we are getting sleepy and better when we do something right after a good night's rest or even just a nap, it's likely that that is the main reason these results were obtained. The same problem can be found in this line of reasoning:

""The more slow wave activity the sleeping participants had, the better their memory was during the recall test 10 hours later," Born said. Scientists have long thought that sleep is important in memory consolidation. The authors suggest that the brain's prefrontal cortex "tags" memories deemed relevant while awake and the hippocampus consolidates these memories during sleep. "

The more relaxed the participants were able to become, the better their subsequent performance was. It's a gross simplification of deep sleep to reduce it to a mere memory-consolidating phase and other benefits from more deep sleep are bound to have a considerable effect.

The only part that could tell us something, IMO, would be:

"The researchers also recorded electroencephalograms (EEG) from the individuals who were allowed to sleep. They found an increase in brain activity during deep or "slow wave" sleep when the volunteers knew they would be tested for memory recall. "

And I find even this to be highly susceptible to demand characteristics. "Hmm I was told earlier that I'm gonna be tested and now they want me to go to sleep. I probably should make sure I get a good rest so I can do better next time!" vs "Hmm so I just did this test and now they want me to sleep? Okay I guess" or something like that.

This isn't so much criticism aimed at the original report as it is criticism at how, when scientific findings are to be reported by popular outlets they are often so trimmed that almost all value is lost and all that's left is "hey look these researchers say that this thing happens!". I understand that there's a need for simplified reports, but I really think they can do better than this (and sometimes they DO, of course)

Quote:Original paper's not online yet; till then I'll have to wonder how they eliminated consideration of the waking time between informing them and taking the test.

I'm doing a thesis on sleep and memory consolidation. Normally how they deal with this problem is testing in the morning and 8 hours later for the wake group, and in the night and 8 hours later for the sleep group. This does have the problem of possible circadian effects though. Other studies test one group later the same day, and the other group the next day, or use sleep deprivation.

There have been a few studies already that deal with explicit versus implicit encoding and consolidation in sleep (more have dealt with procedural versus declarative memory).

Awareness modifies the skill-learning benefits of sleep
Anticipated reward enhances offline learning during sleep.
The prefrontal cortex and cognitive control

The consensus seems to be that if you know you are going to be tested/want to remember something, and therefore explicitly formulate what you have to remember, you benefit more from sleep. The mechanism for these things is not fully known but it's likely a dialogue between the prefrontal cortex and hippocampus which occurs during sleep but not wakefulness (you need "offline" time to consolidate memories because other things are encoded during wakefulness).

Very interesting links, thank you. I notice Jan Born is a rather prolific author of these sleep studies.

Perhaps artificial induction of sleep would've been useful in this study. Or can they do that. ;p

This seems relevant: ‘The role of sleep in declarative memory consolidation: passive, permissive, active or none?’

They can induce sleep by basically shocking the front part of the hypothalamus, but I think they've only done that in rats, because you have to stick the electrode very deep into the brain. In humans, though, they change what sleep stage you are in to a degree just by stimulating the outer cortex. It can increase the amount of slow wave activity (but interestingly not spindles or bursts) which improved declarative memory (but not procedural memory, which might be consolidated in REM sleep?) according to another of Born's studies .

Transcranial Direct Current Stimulation during Sleep Improves Declarative Memory

I'll read that paper you mentioned, looks interesting. There are certain people who are really "famous" in sleep it seems, and Stickgold is one of them.

Quote:They found an increase in brain activity during deep or "slow wave" sleep when the volunteers knew they would be tested for memory recall. "

And I find even this to be highly susceptible to demand characteristics.

People can't willingly change their level of slow wave activity, and it doesn't reflect level of "relaxation" or anything like that, it's a mathematical value you calculate from the EEG. Studies have been done where people or rats learn something which uses a certain part of the brain (ex. temporal lobe of cortex) and they have seen that SWA increases in that part where the learning occured during sleep. There's a lot of suggest that increased SWA is a response to learning, from outside this study.