Sleep's memory role discovered | Hacker News Reader

Sleep's memory role discovered

bbc.com

125 pointsLibertatea27 comments

The paper can be found at [1]. This is not a completely new finding. We have know that motor learning induces spine formation for quite awhile. What is novel is comparing to the sleep deprived condition and seeing effects on structural plasticity. However, there is still a long way to go to causally link increased spine formation to improvements on memory and motor tasks. We like to think that spines represent a structural correlate of memory (and they probably are), but there are a whole bunch of open questions that need to be answered before we can actually prove that claim.

1. http://www.sciencemag.org/content/344/6188/1173.full

Does this have to do with LTP? I feel like meditation and NMDA antagonists can sometimes mimic the function of a good nap for me.

Little anecdata that agrees with your sentiment: I did regular meditation sessions almost daily (basic concentration exercise where you focus on breathing) throughout my middle school and high school years and finished high school with highest grade average possible (that was in Vienna, Austria). It was even more surprising as the time that I felt was necessary to invest in order to achieve these grades went down over the years and not up.

So LTP is generally thought to be mediated by an increase in the number of AMPA receptors at a synapse. There have also been studies showing that the size of spines is correlated with the number of AMPArs present at the synapse. Whether LTP actually induces the formation of more spines is not entirely clear. The general answer is 'we think the processes are probably related' but it is difficult to do the experiments needed to show that the in vivo correlates of LTP actually cause increased spine formation as part of their downstream signaling pathways. It is worth noting that most of our knowledge about LTP comes from studies in the hippocampus and that the relation between spine formation and LTP may vary from brain region to brain region and even from cell type to cell type.

tl;dr It is hypothesized that increased numbers of spines is a later stage of the process of memory consolidation that may initially appear as LTP however we need a whole lot more evidence to support those hypotheses.

This seems a little sensationalist. No, the memory role of sleep was not "discovered": a paper proposing a credible theory was published, based on experiments performed on mice. Moreover, the proposition that is being advanced by the paper --- that specific sleep phases strengthen particular neural connections --- has already been made previously, and is generally suspected to be true in academic circles anyway. So the publication of this paper constitutes nothing more than a few (perhaps important) results supplying a bit of further evidence in favour of an already well-supported hypothesis; that is all.

Do you have some good reference about this hypothesis? I'm not really into neuroscience but this really interests me. I'm more on the machine learning side with artificial neural networks, but I often wondered whether some sleep-like phases could get me some improvements. Of course, the question is, what exactly should happen in that phase. What particular neural connections should I strengthen?

Perhaps it has no analogous to software neural networks?

Looks like this "strengthening" is needed because there's actual "matter", "tissue" etc involved.

from what i recall (no documentation link, but it's been posted here before) strengthening is more about making associations/connections for the things that are important. so if you have CPU bound batch jobs that run each night for identifying new connections between clusters of data... it seems like it'd be pretty analogous. it's not like things we 'forgot' weren't stored, or somehow dropped from memory; we just couldn't access it when we needed to later, and once reminded we're fully aware.

there's also been studies on people who suffer a traumatic experience; if they're deprived sleep following the event then the memories are less severe/traumatic.

By "discovered" I assumed more of like "deepened knowledge of". I guess I'm so accustomed to sensationalist titles by now that I immediately tone it down to more realistic version in my head and don't even notice.

When I studied for university exams, I used two-phase sleep cycle. I studied from 10 AM to about 3 PM, then I had a 3-hour nap to about 6 PM, and then I continued to study from about 7 PM to 11 PM.

I can wholeheartedly recommend it; it's quite efficient and you can easily adapt to it from your normal single-phase cycle.

I'm sorry but you didn't provide enough data on your sleep. Basically you're telling us you took a long nap in the afternoon. How much sleep did you get at night?

Well, this was like a decade and half back, so I don't have "enough data". :-) You're right, that's what I am saying. I think I just got the amount of sleep I needed at night (which means I woke up at around 7). This is not a technique to reduce sleep, but to learn better.

So, you slept 11 hours a day?! Wow.

Take it further to the Dymaxion model - half an hour of sleep every 6 hours!

So if memories are being replayed, where are the memories coming from and to where are they being persisted?

Is it like a backup is being formed from more short-term memory to more long-term memory? Are long-term memories being replayed to ganglia responsible for "muscle memory" to improve response times?

How could you test for something like that? Maybe, teach an array of skills, and for each skill with subjects of varying degrees of sleep deprivation and for varying time intervals between education and performance, measure response times and skill level in the tasks?

One way this 'replay' effect was tested was in rats where they implanted many electrodes into the animal's hippocampi to monitor activity. There are cells there called the hippocampal place cells which encode locations in space.

Then they had the rats run a simple circular maze with some landmarks (food, etc.) at various points. As they run the maze, different place cells start to encode different locations in the maze, especially near the landmarks, and they activate when the rat is near there.

They kept the electrodes in while the rat was sleeping. They found that the place cells continued to activate in the same order as the locations in the maze, as if the rat were actually running the maze in, e.g., a clockwise direction.

This is taken as evidence that, during sleep, the rat's brain was replaying the memory of running the maze.

Source:

Skaggs, William E., and Bruce L. McNaughton. "Replay of neuronal firing sequences in rat hippocampus during sleep following spatial experience." Science 271.5257 (1996): 1870-1873. (http://wws.weizmann.ac.il/neurobiology/labs/ulanovsky/sites/...)

Recent memories (so-called 'hippocampus-dependent memories') are stored in the hippocampus for up to about two weeks, during which time they are gradually transferred into permanent storage in the neocortex, cerebellum, and other parts of the brain. So, to answer your question, that is where they are replayed from.

The hypothesis is that the hippocampus is unique in being able to store memories quickly and after a single exposure. Most of the rest of the brain needs time and repeated exposures to store a memory via long-term potentiation. The role of the hippocampus is to act as a buffer where memories are kept temporarily.

While you're sleeping, your hippocampus repeatedly activates the memory, stimulating the brain in a similar way that the original event did. Slowly, the neocortex begins to rewire itself through synaptic plasticity to store the memory. After many repetitions, the memory is no longer dependent on the hippocampus and it fades away.

I think this is the paper I'm recalling this from, but I'm not entirely sure (this memory is several years old):

Bontempi, Bruno, et al. "Time-dependent reorganization of brain circuitry underlying long-term memory storage." Nature 400.6745 (1999): 671-675.

A couple of days late, but thanks for the explanation.

I can tell you, as a person who suffered (and I mean Suffered) insomnia for 8 years, and saw countless docs.. (the cause was stress, and docs don't treat that) .. the role for me is that it makes it work like I am a teen again. I can memorize youtube urls now, with some practiced chunking.

I had a similar discovery with sleep myself like that. I had been suffering from un-diagnosed severe complex sleep apnea for as best as we can figure 5-10 years. once starting sleep with a BiPAP machine to help with the breathing I went from having no REM sleep and no dreams to having them all the time. After about the first month I could finally remember what happened the day before clearly and without issue. The dramatic change did actually swing me a little more towards depression for a while simply because I could finally understand what I had been missing for so long and that there was nothing I could do to get it back. It was definitely an interesting experience.

I know that depression increases the need for sleep and napping. I also remember reading of evidence that long term depression shrinks the hippocampus. Could the increase in need for sleep indicate a poorly functioning hippocampus under conditions of depression? And could such a connection, if it exists, be an avenue for finding better chemical (or electrical) treatment for depression?

I was going to comment but decided that a nap was more important

And yet you still commented. The nap can't have been that important after all ;-)

Unless it was a sleep-induced comment. Their memory was just an empty text box waiting to be filled.

Or perhaps the post came during the nap!

http://xkcd.com/269/

great excuse to bring sleep bag to work.

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