Neuroscience: News and Discussions.
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Is the Purpose of Sleep to Let Our Brains “Defragment,” Like a Hard Drive? (blogs.discovermagazine.com)
submitted 11y ago by camilstoenescu
MIBPJ 2 points
Interesting article but here are a few inaccuracies/misinterpretation:
The glutamate receptor which is inserted and which underlies memory formation is called an AMPA receptor. If memory serves me correct, only about 2% of AMPARs allow calcium through. Granted, many people think that the calcium premeable AMPARs are responsible for memory formation, but these are quickly swapped out in a process independent of sleep.
Also, synaptic scaling is not universally accepted as actually occurring in the brain (at least during normal functioning). The main evidence in support of synaptic scaling in vivo and in mammals comes from studies which show that when you close an animal's eye for several days that there appears to be synaptic scaling in the visual cortex. One problem with synaptic scaling is that is destabilizes recurrent brain networks (network in which there are connections between neurons in the same brain area and not just connecting brain area A to area B). Since the brain is almost entirely recurrent, it is not clear how synaptic scaling could actually work without the brain going into seizures all the time.
These are just some minor issues, but overall that is a great blog post!
The glutamate receptor which is inserted and which underlies memory formation is called an AMPA receptor. If memory serves me correct, only about 2% of AMPARs allow calcium through. Granted, many people think that the calcium premeable AMPARs are responsible for memory formation, but these are quickly swapped out in a process independent of sleep.
Also, synaptic scaling is not universally accepted as actually occurring in the brain (at least during normal functioning). The main evidence in support of synaptic scaling in vivo and in mammals comes from studies which show that when you close an animal's eye for several days that there appears to be synaptic scaling in the visual cortex. One problem with synaptic scaling is that is destabilizes recurrent brain networks (network in which there are connections between neurons in the same brain area and not just connecting brain area A to area B). Since the brain is almost entirely recurrent, it is not clear how synaptic scaling could actually work without the brain going into seizures all the time.
These are just some minor issues, but overall that is a great blog post!
NedDasty 5 points
It's AMPAs with the GluR2 subunit that allow Ca^(2+) through due to Q->R editing (which occurs at nearly 100% of GluR2 subunits).
I also hate it when people try really hard to make analogies to methods used by computers. The only relation between a hard drive and a human brain is one of their functions: to store information. Our brains don't have platters, they don't have spindles, and they don't have sectors. As far as we know, our brains don't have minimum allocation unit sizes. When our brain stores a memory, I doubt it searches through the brain for a "free" location and, if the size of the memory exceeds any free spot, splits up the memory and puts it into different locations.
That is an absurd, complicated method. Trying to make the analogy is, IMO, trying to force a square peg into a circular hole.
I also hate it when people try really hard to make analogies to methods used by computers. The only relation between a hard drive and a human brain is one of their functions: to store information. Our brains don't have platters, they don't have spindles, and they don't have sectors. As far as we know, our brains don't have minimum allocation unit sizes. When our brain stores a memory, I doubt it searches through the brain for a "free" location and, if the size of the memory exceeds any free spot, splits up the memory and puts it into different locations.
That is an absurd, complicated method. Trying to make the analogy is, IMO, trying to force a square peg into a circular hole.
MIBPJ 2 points
Unless I'm misreading you, I think you have your AMPA facts mixed up a bit. GluR2 subunits render the AMPAR calcium **impermeable**, not the other way around. Here is from a Stuart Cull-Candy review, "One of the most striking of the RNA editing changes affects the GluR2 subunit, resulting in a glutamine (Q) to arginine (R) switch at the ‘Q/R site’ in the pore-lining (M2) region. Editing at this site is nearly 100% efficient, profoundly altering the properties of GluR2-containing AMPARs, rendering them Ca2+-impermeable."
While I agree that the computer analogies confuse more than they clarify, I think that in this case its not a bad analogy. In both cases your compressing and restoring information in a way that allows the brain/computer to process new information more effectively. An analogy doesn't have to be perfect for it to be useful, especially when explaining complex concepts to laymen.
While I agree that the computer analogies confuse more than they clarify, I think that in this case its not a bad analogy. In both cases your compressing and restoring information in a way that allows the brain/computer to process new information more effectively. An analogy doesn't have to be perfect for it to be useful, especially when explaining complex concepts to laymen.
NedDasty 2 points
Yeah, misspoke about the GluA2s, my bad.
As for the analogy: analogies are good for representing difficult concepts by relating them to something familiar. I think an analogy is being forced here, when that is not really the case. I guess I'm not that strongly against this particular analogy, it sort of makes sense. But the author of this article has some really, really bad ones, for example, this gem:
>It’s as if each neuron were a cup, and each synapse corresponds to a different liquid. During the day, memories form and certain synapses get stronger, which means pouring more of those particular liquids into the cup. At night, synaptic scaling pours some of the mixture back out, bringing it back to the baseline level without changing the relative proportions of the mix.
That analogy sucks, haha.
As for the analogy: analogies are good for representing difficult concepts by relating them to something familiar. I think an analogy is being forced here, when that is not really the case. I guess I'm not that strongly against this particular analogy, it sort of makes sense. But the author of this article has some really, really bad ones, for example, this gem:
>It’s as if each neuron were a cup, and each synapse corresponds to a different liquid. During the day, memories form and certain synapses get stronger, which means pouring more of those particular liquids into the cup. At night, synaptic scaling pours some of the mixture back out, bringing it back to the baseline level without changing the relative proportions of the mix.
That analogy sucks, haha.
MIBPJ 2 points
Hahah that one is especially bad. I do agree though, people do get carried away with the brain=computer analogy. Its a nice metaphor for explaining difficult concepts in an easy to relate to way, but to use that analogy to guide research is a bit silly.
etatsunisien 0 points
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