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I've seem several articles claiming that sleep is akin to the usual proccess of hard drive defragmentation, however for your brain. This process allegedly prunes synapses/memories and reconsolidate memories.

You can find several versions of this claim:

(..) So the brain must periodically clear out the synaptic underbrush—analogous to “running a repair-and-cleaning program on your computer to defrag the hard drive,” says psychologist William Killgore of Harvard Medical School. http://time.com/4737596/sleep-brain-creativity/

(...)A defrag consolidates the same data into a more logical order. Defragmentation is a taxing chore for the computer, so many people schedule it to happen overnight. In the same way, sleep may serve to reorganize and reconsolidate memories. http://blogs.discovermagazine.com/neuroskeptic/2011/08/21/is-sleep-brain-defragmentation/#.XIg-xbjQ-Uk

(...) During sleep, your brain goes into a cleansing and restorative mode. It washes away all of the unimportant and unnecessary thoughts and memories to maintain space for all the memories you need to function, and reorganizes the free space for new memories you’ll make tomorrow. In a nutshell, your brain gets refreshed when you sleep. And this process is so important because it aids in the healing of dementia. http://handsoffmybrain.com/2018/09/defrag-your-brain-with-sleep-but-what-do-you-do-if-you-cant-sleep

Does the brain do something similar to defragmentation while we sleep, by cleaning synapses and "washing away" unimportant thoughts?

T. Sar
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    What sort of evidence would it take to convince you it was or wasn't a "valid analogy"? I could argue that human memory isn't like a disk drive, in that it doesn't assign specific neurons to specific memories, so defrag analogy is invalid, or I could argue that there is a "consolidation" during the REM cycle, so the defrag analogy is helpful. Is this not just opinion-based? – Oddthinking Mar 12 '19 at 23:55
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    @Oddthinking I'll edit that out, if it is causing problems. I don't see it as opinion based - there are several places saying "X", and I'm asking if "X" is true. – T. Sar Mar 13 '19 at 00:29
  • @Oddthinking That said, defrag is defined as reorganization of data around a memory storage device for faster access. An answer would either prove or refute this, by showing how similar or different sleep is from actual defragmentation. – T. Sar Mar 13 '19 at 00:31
  • Where is it defined liked that? For example [dictionary.com](https://www.dictionary.com/browse/defragment) defines it as "to reorganize files on (a disk) so that the parts of each file are stored in contiguous sectors on the disk, thereby improving computer performance and maximizing disk space." The brain doesn't have contiguous sectors, so it is not literally defragging. It is still an analogy though. – Oddthinking Mar 13 '19 at 01:12
  • As all your references show, this is the current thinking. The actual mechanism of "reorganization" during sleep is only beginning to become understood, so "defrag" is as reasonable a metaphor as one could hope for. A good layman's source for info on the topic is [Why We Sleep](https://www.barnesandnoble.com/p/why-we-sleep-matthew-walker-phd/1125897958/2661376945258?st=PLA&sid=BNB_ADL+Marketplace+Good+Used+Books+-+Desktop+Low&sourceId=PLAGoNA&dpid=tdtve346c&2sid=Google_c&gclid=Cj0KCQjwsZ3kBRCnARIsAIuAV_TjtdLpFTVb5uUn2FzzGrbtT-3w9gVMBVUzLZfUuNUhQ5iYW5V5GNoaApHfEALw_wcB) by Matthew Walker. – Daniel R Hicks Mar 13 '19 at 01:12
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    'there are several places saying "X"' - I don't think any are saying "A is equal to B". They are saying "A is analogous to B." An analogy isn't true or false - it is helpful to understanding or not helpful to understanding. – Oddthinking Mar 13 '19 at 01:14
  • Please quote (at least) one of the sources. As is, we have your summary and then a list of links. What is the exact claim in their words? – Brythan Mar 13 '19 at 06:39
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    Seems like a great analogy to me as it explains a function of sleep in familiar terms. But it is an abstraction, which you are treating as concrete in your question. Steven Novella has written some articles on the subject. I like this one, which shows how sleep deprivation can have an adverse effect on memories: https://theness.com/neurologicablog/index.php/sleep-and-false-memory/ – Jerome Viveiros Mar 13 '19 at 08:20
  • @Oddthinking "reorganization of data around a memory storage device" = "to reorganize files on (a disk) so that the parts of each file are stored in contiguous sectors on the disk" / "for faster access" = " thereby improving computer performance". Your definition is synonymous to mine, albeit a little more complete. I honestly doesn't understand your criticism. Is it because I paraphrased it? – T. Sar Mar 13 '19 at 11:35
  • @Oddthinking I scoped down to three more focused excerpts from the bigger references and prunned out the lesser ones. – T. Sar Mar 13 '19 at 11:49
  • @JeromeViveiros I'm not treating it as a concrete thing; I know very well that this is just an analogy. That said, the analogy might be utterly wrong - the brain can be doing something completely different from a defrag, without anything even remotely related to memory prunning/reconsolidation. – T. Sar Mar 13 '19 at 11:53
  • Everything I've read (see Mathew Walker's book, eg) suggests that the analogy is a good one. – Daniel R Hicks Mar 13 '19 at 12:11
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    I think the criticism is that you are taking the analogy too literally. It's a good analogy in many ways, but *not* meant to be taken literally. A hard drive *never forgets in the first place*, unless defective or ordered to delete data. A defrag on a hard drive is solely for faster access. The brain operates fundamentally differently, but it also has this function that works much better during a time of low activity, and which also is "reorganizing" in a way. It's a good analogy, IMHO, but your question "is it true?" is from a false premise. No-one actually made the claim you're skeptical of. – DevSolar Mar 13 '19 at 13:11
  • @DevSolar I'm skeptical that the brain uses sleep to clear synapses and consolidates its memories, as claimed in the excerpts. It isn't the analogy per se the issue. I've clarified the question. – T. Sar Mar 13 '19 at 13:54
  • I find it amusing that people are reading the comments but aren't actually reading the question to see that most of the raised issues are already solved or clarified. – T. Sar Mar 13 '19 at 14:15
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    @T.Sar they might also be reading the title, which still reflects the old question. – TheWanderer Mar 13 '19 at 15:31

1 Answers1

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There is a plethora of scientific work that all points towards sleep being very important for the kind of cleanup and reorganisation you are referring to.

Information like this is readily available e.g. at WP:Sleep#Functions. I've enriched this with a couple things I found in the German Wikipedia, not linked from the above "Sleep" page:

1) The brain / glymphatic system is much more efficient at chemical "clean up" during sleep.[1]

A publication by L. Xie and colleagues in 2013 explored the efficiency of the glymphatic system during slow wave sleep and provided the first direct evidence that the clearance of interstitial waste products increases during the resting state. [...] Xia and Nedergaard demonstrated that the changes in efficiency of CSF–ISF exchange between the awake and sleeping brain were caused by expansion and contraction of the extracellular space, which increased by ~60% in the sleeping brain to promote clearance of interstitial wastes such as amyloid beta.

2) Sleep promotes branch-specific formation of dendritic spines after learning.

These findings indicate that sleep has a key role in promoting learning-dependent synapse formation and maintenance on selected dendritic branches, which contribute to memory storage.

3) Sleep inspires insight.

Insight denotes a mental restructuring that leads to a sudden gain of explicit knowledge allowing qualitatively changed behaviour. [...] Sleep consolidates recent memories and, concomitantly, could allow insight by changing their representational structure. Here we show a facilitating role of sleep in a process of insight.

At which point I stopped collecting more references, simply because there are so many and the claim is thoroughly confirmed.

DevSolar
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  • Thank you for your answer. I find the first article (the one about chemical cleanup) specially interesting. This is exactly what I was looking for. – T. Sar Mar 13 '19 at 14:24
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    @T.Sar The chemical cleanup hypothesis of sleep is possibly quite different from the process you described in your OP as "prunes synapses/memories and reconsolidate memories" - I would say in the field right now they are essentially opposite hypotheses of the purpose of sleep. That said, I don't think they are actually mutually exclusive but it would be a mistake to consider them synonymous. – Bryan Krause Mar 13 '19 at 16:00