Neuroscientists' New Theory: Dreaming Protects the Braincells For Eyesight (time.com) 73
Writing in Time magazine, two neuroscientists share a surprising new theory on exactly how dreaming protects our brains:
Neuroscience used to think that different parts of the brain were predetermined to perform specific functions. But more recent discoveries have upended the old paradigm. One part of the brain may initially be assigned a specific task; for instance, the back of our brain is called the "visual cortex" because it usually handles sight. But that territory can be reassigned to a different task... Recent decades have yielded several revelations about livewiring, but perhaps the biggest surprise is its rapidity...
In the ceaseless competition for brain territory, the visual system has a unique problem: due to the planet's rotation, all animals are cast into darkness for an average of 12 out of every 24 hours... So how did the visual cortex of our ancestors' brains defend its territory, in the absence of input from the eyes? We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our "defensive activation theory," dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory...
REM sleep is triggered by a specialized set of neurons that pump activity straight into the brain's visual cortex, causing us to experience vision even though our eyes are closed... The anatomical precision of these circuits suggests that dream sleep is biologically important — such precise and universal circuitry rarely evolves without an important function behind it... We suggest that dream sleep exists, at least in part, to prevent the other senses from taking over the brain's visual cortex when it goes unused. Dreams are the counterbalance against too much flexibility.
Thus, although dreams have long been the subject of song and story, they may be better understood as the strange lovechild of brain plasticity and the rotation of the planet.
In the ceaseless competition for brain territory, the visual system has a unique problem: due to the planet's rotation, all animals are cast into darkness for an average of 12 out of every 24 hours... So how did the visual cortex of our ancestors' brains defend its territory, in the absence of input from the eyes? We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our "defensive activation theory," dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory...
REM sleep is triggered by a specialized set of neurons that pump activity straight into the brain's visual cortex, causing us to experience vision even though our eyes are closed... The anatomical precision of these circuits suggests that dream sleep is biologically important — such precise and universal circuitry rarely evolves without an important function behind it... We suggest that dream sleep exists, at least in part, to prevent the other senses from taking over the brain's visual cortex when it goes unused. Dreams are the counterbalance against too much flexibility.
Thus, although dreams have long been the subject of song and story, they may be better understood as the strange lovechild of brain plasticity and the rotation of the planet.
dreams are (Score:5, Funny)
a keep alive function
FP!
Other theories (Score:2)
The brain is doing backprop and sparsifying the network. You can't run the backprop when your awake because the network is processesing the current visual input. To be able to back prop to the input you need to have the input be quiet. By activating neurons deep in the layers of the brain you can then have inhibitory signals from active neurons suppress less active neurons. Thus the neural recognition pattern becomes concentrated into a sparse set and thus closer to a classificaitonor decision or recogn
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The problem with any theory that propose to "explain" why dreaming, or sleep, exists is that unless it explains all of the other evidence on the subject that points to other functions then it fails in any claims to be a complete theory. The known necessity of neural networks to prune, and the sorts of bizarre mental malfunctions that quickly arise in people who cannot dream suggest that clean-up is surely a key role of dreaming.
This theory might have some validity as one of the things that dreams do - but t
Re: Other theories (Score:1)
The problem with any theory attempting to explain why is that biology often doesnâ(TM)t have a why. It just happens because it works. Dreaming my do all kinds of things⦠because.
Re: Other theories (Score:4, Insightful)
Wrong kind of "why". Biology generally has a reason why something developed that is not the same as why the sentient entity values it. There is the general "it survived accidentally" reason (meteor hit and it was on the other side of planet at the time), but there may also be more specific reasons for the survival (it had longer neck and could reach more food). When we ask "why dreams?" we shouldn't ask what benefit we get from dreaming now but more why did dreaming make us more fit to survive. The answers may be quite different.
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Agreed. Preservation of the visual cortex may well be A function of dreaming, but other evidence suggests it is not THE single purpose of dreaming.
If it were THE purpose, then REM deprivation should primarily result in a loss of visual acuity. However, we know that other negative effects are sufficiently prominent that the theorized effect on visual acuity goes unnoticed.
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We also know of various animals that go months with no light in the far north, who don't loose the use of their visual cortex.
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However, REM sleep is not where "Clean-Up" occurs. It occurs in the Deep/Non-REM stage.
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But it is where most dreams happen. Indeed, slow wave sleep is thought to involve metabolic clean-up and it is thought that some dreaming may occur then. Night terrors happen in slow wave sleep. But that's all further evidence that maintaining the visual cortex is far from the sole purpose for dreaming.
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The cross correlational memory storage of sensory input patterns as associated with past sensory inputs, to help to create and improve decisions associated with positive outcomes for the sensory input patterns. The fun bit, it is hugely distorted by 'FANTASY' content, the unreal content we consume, the idiot box and it's sensory inputs, strange dreams. Also due to quantum consciousness it is more impacted by that shared conscious state of all us quantum consciousnesses versus the conscious state. With two d
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Pop science (Score:5, Interesting)
Notice that the scientist is publishing in Time Magazine. He's pushing his theory (and his new book) for all it's worth, and other scientists are taking issue with it.
Just as my own anecdotal evidence, many of my dreams are tactile in nature, which doesn't fit his theory at all. And many of his assertions (WHO declares health emergency due to sleeplessness!) are simply not true.
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Uh, that's not a dream. You wake up with sticky hands.
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Yup, had a nice hot one last night.
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Rosy Palm visited.
Re:Pop science (Score:5, Insightful)
Healthy skepticism is fine, but i find it a refreshing thought.
And even if not right, goes to show there may be plenty things that make perfect sense yet just no-one thought of it yet. It surely is an elegant explanation.
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I saw the Black Eyelids movie. The book was better.
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Then we have the night vision problem, if our visual cortex is so active, why do we have to adjust vision for a while when waking up?
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Your brain doesn't really work that way. It's really quite plastic. If you are born blind, or become blind, your visual cortex doesn't just sit there, it gets co-opted by other functions. We don't really know the details of how this happens, but neuroscientists have observed that neurons like to connect to other neurons that are active. If it's insufficiently stimulated, parts of your visual cortex (or any other part of your brain) will start establishing connections with neighbouring areas that are active.
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If you are born blind, or become blind, your visual cortex doesn't just sit there, it gets co-opted by other functions
Maybe in the same way that a screwdriver, in the absence of screws, can be used as a pry bar. It's still the same tool. It doesn't get used for entirely unrelated things. It gets used for spatial processing - whether that's music, math, or perceiving the shape of your surroundings by sound.
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Sure, or language or solving math equations. https://www.sciencedirect.com/... [sciencedirect.com]
Re: Pop science (Score:2)
We do observe the visual cortex region being repurposed in blind folks, both blind from birth and blinded in childhood. I am not aware of any studies looking at this in adults. I can easily imagine REM developing first to preserve sight in kids while brain functions are being allocated, then REM just happens to have a nice side-effect for cognition and so adults who retain REM after childhood become more fit to survive. I don't know how to study that process.
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Notice that the scientist is publishing in Time Magazine. He's pushing his theory (and his new book) for all it's worth, and other scientists are taking issue with it.
Just as my own anecdotal evidence, many of my dreams are tactile in nature, which doesn't fit his theory at all. And many of his assertions (WHO declares health emergency due to sleeplessness!) are simply not true.
As noted in the Times article, he previously published his findings elsewhere. Choosing to publish a popular book-version of research may not endear him to other scientists, but, it's been done by many others in the scientific community. Criticisms of that decision are not a valid refutation of his findings.
Without assuming his theory is proven, or even valid, but, starting with it, tactile factors in dreams could be the brain completing the experience. Most of our experience of reality is m
Re: Pop science (Score:2)
The big theory with his problem for me is that sleep apnea doesnâ(TM)t cause blindness. People can go for years without REM sleep and not lose their vision.
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> People can go for years without REM sleep and not lose their vision.
They cannot live for years without REM. Being without dreaming for even a few days is very disorienting, even destructive. There is some interesting work that if sleep deprived, or denied REM, people will enter REM _much faster_ when they fall asleep, which can help keep people alive and somewhat functional even when sleep deprived.
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That is a reasonable point, My point was that humans do not survive without REM sleep. It speaks against the theory.
Re: Pop science (Score:2)
You raise an interesting objection. I would be curious to look at vision problems in kids with sleep apnea. The brain loses plasticity in adulthood, and enough adult systems might keep the vision center exercised despite loss of REM. But in kids, where we observe huge shifts in brain allocation based on stimuli, I can see possibly bigger problem. It would be a good way to investigate this hypothesis, I think.
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Many people I know have (levels of) aphantasia ( https://www.bbc.com/news/healt... [bbc.com] ), including myself. In my case that means that I see only black when I dream.
I sleep well and can still see during the day, so why hasn't my visual cortex been taken over during all those nights in the past decades?
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Nature's screen-saver (Score:4, Funny)
Nature's screen-saver
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Forget screensavers; this is a golden opportunity to insert unavoidable advertising in your brain!
I really want to be wrong, but I have suspicions I'll be very unpleasantly correct before the end of my lifetime.
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Window users get a BSOD.
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BSOD? I had those, they'll called "nightmares"
Nightmares (Score:2)
So what are nightmares then? Do nightmares protect the eyesight to then scare the crap out of the rest of the brain? Probably best not to ask, or that's going to be a nightmare...
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Nightmares are your brain's attempt to fight off those areas from taking over the visual cortex.
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Nightmares are your brain's attempt to fight off those areas from taking over the visual cortex.
No, it's already what dreams do. I was asking specifically about nightmares, because these can keep people awake or wake them up. Current science classes nightmares and night terrors as a sleep disorder, but their occurrence is so frequent among young people that it doesn't seem like a simple disorder, or else would evolution have sorted it out and reduced it down to rare cases. Jumping up in the middle of the night, screaming and walking around half-asleep doesn't strike me as a strategy for survival. Bein
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Jumping up in the middle of the night, screaming and walking around half-asleep doesn't strike me as a strategy for survival.
It might if it startles the predators and enemies sneaking up on you in your sleep.
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It might if it startles the predators and enemies sneaking up on you in your sleep.
If so then it should work just as well when one is awake. Something tells me though it's a pretty bad idea to give it a try. I wouldn't want to walk into a lion camp at night and then try to shush them away to test your theory.
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Nightmares seem to have a function of their own.
That's why I used the term fight. While dreams keep the visual cortex active in an effort to prevent those other areas from intruding into it, nightmares are your brain fighting off those attempts. Nightmares generally wake up people who in turn open their eyes. Thus, the visual cortex is used.
It's your brain's way of saying, "Back off! I'm not afraid to use this."
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While dreams keep the visual cortex active in an effort to prevent those other areas from intruding into it, nightmares are your brain fighting off those attempts.
It doesn't convince me and the focus on the visual cortex is too limiting in the case of nightmares. I'm happy to accept the visual cortex theory as an explanation for dreams, but otherwise are nightmares a bad survival strategy, and nightmares are also often linked to past traumas.
If it is about the visual cortex then perhaps the process that feeds the visual cortex (to keep it active) simply cannot distinguish between good and bad memories, chooses at random and whatever is fresh in memory, and so where b
Re: Nightmares (Score:2)
Evolution does not sort things out if no better solution arises by chance. Live childbirth is fairly dangerous to individuals, especially compared to egg laying, and yet live births continue for other reasons. Nature has not developed a more sentient umbilical cord that knows how to avoid wrapping a baby's neck, for example. Many problems persist not because they are a global maxima but just because they are a local maxima!
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Evolution does not sort things out if no better solution arises by chance.
What are you saying? That nightmares have a purpose? If so then I'd like to read what your reasoning is. Just explaining how evolution works doesn't explain how nightmares fit in with this new theory and just ends being a deflecting from the topic. I've mentioned survival strategy to remind of the evolution process. If all you're then saying is that the sky is blue, water is wet, and how evolution works then thanks, but it's not really helping unless you do have a better answer.
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I am saying that nightmares might NOT have a purpose. I was responding specifically to this statement from you: "or else would evolution have sorted it out and reduced it down to rare cases" -- that is not true. Nightmares might have a purpose that we have not figured out, but it is also possible that they are just a defect, a widespread disorder. Evolutionary processes do not necessarily solve widespread disorders... evolution propagates the most successful design among the designs available . It does not
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I was responding specifically to this statement from you: "or else would evolution have sorted it out and reduced it down to rare cases" -- that is not true.
That's not what I was saying. You've taken the statement only out of context, which was that of nightmares being a sleep disorder. When we classify mental processes as disordered, then it implies that an ordered state exists, thus there is a better solution as you say.
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When asked... (Score:2)
When these two were asked about the likelihood that their theory will be proven true, one responded, "I can dream, can't i?"
We dont move much during sleep either (Score:2)
So how come the motor cortex doesnt get taken over? Sorry, this theory doesnt sound very convincing to me.
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The pons shuts off signals to your spinal cord during REM sleep. Otherwise you'd act out your dreams, which some people do when this mechanism is broken.
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I think you're forgetting something. (Score:3)
At least motor planning and various circuits are active also.
These are usually paralysed from actually outputting to the body - a form of normal sleep paralysis that goes away on waking.
Not all the body is paralysed - eye movement still occurs.
Defend its territory? (Score:2, Informative)
12 hours isn't very long.
It also isn't very accurate, in that much of the time there's enough moonlight to do stuff outside, so primitive man could function at night at least a quarter of the time.
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Even if up late, you still have to sleep eventually.
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I just don't see having part of the brain be nominally idle during sleep as a big problem. If it's important enough while you're awake, you're not going to evolve towards its compromise.
Analog MUX (Score:2)
Reason for dreaming may be better learning (Score:3)
I remember learning about Hinton's restricted boltzmann machines back when I was at U of T. For those who aren't familiar with RBMs, they're a very simple type of neural network that only has two layers of neurons -- "visible", and "hidden" layers. The visible neurons are exposed to the data, and light up the neurons in the hidden layer. The connections between them would be weighted in a way to use the least "energy" possible. Pretty simple.
A net like this would learn by showing it data, activate the hidden neurons, randomly change some hidden neurons, send these activations back down to the visible layer, then activate the hidden neurons again a second time. Now, make the corrections to the weights.
But, a better way to learn (net learns faster) was to bounce activations back and forth many many more times before correcting the weights.
What's amazing is you could see the output of this visible layer. It would be a recreation of what the net remembered. If you bounce the activations up and down several times without it learning you would (for example) see a ghostly image of the digit "2" twist and warp and float in its box as this very simple neural network "imagined" the number 2. Let it run indefinitely and this net would "dream" about the number 2 indefinitely.
At the time, this suggested to me the idea that the main evolutionary benefit of dreaming was that it speeds up learning. People who use neural nets know that more data is better, but how can your brain learn when it's actually switched off at night? Dreaming basically creates more data for the brain to learn from as activations are bounced between deep and shallow parts of the visual cortex, and when you wake up your brain updates itself with one gigantic weight update. Instead of learning "what is", it learns "what isn't". You may dream of some oddly-shaped bowls or flying rabbits, and when you wake up your brain learns better what bowls look like and how rabbits really move. Most bowls aren't "warpy", and rabbits can't fly (on their own). The downside of this is that if your eyes don't see the thing you dreamed about, your brain can't correct its own imagination.
Anyway, just a thought.
Problem with this theory (Score:2)
Why is dreaming so emotional? For me, the emotional content of dreams, particularly nightmares, is more significant and memorable than the visual experiences themselves.
Re: Problem with this theory (Score:2)
To add to that: the emotional content is often decoupled from the visual experience. On reflection, the emotions I felt in response to the events in the dream make no sense, and sometimes bear no relation to what normal waking conscious experience is like.
Re: Problem with this theory (Score:2)
Also, admittedly, emotions in waking life also make little rational sense, given the reasons why we respond emotionally are not always accessible to us.
Itâ(TM)s not pitch black at night. Even when (Score:1)
Re: Itâ(TM)s not pitch black at night. Even w (Score:1)