To sleep, perchance to dream....?

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While watching CORAL SEA DREAMING, one of my fav DVDs, I noticed some sort of pretty reef fish described by the caption as "sleeping in a mucus bubble". Which I assume answers the question of whether fish sleep.

But then I got to thinking about this whole mechanism of sleep and dreams. We all know that mammals, birds, reptiles, amphibians, and even fish sleep. But when we get to the invertebrate level, is sleep still part of the picture?

I somehow doubt this would apply to, say, bivalves, jellyfish, corals, sponges, earthworms, protozoa, and bacteria.... but what about "higher" inverts such as insects, arachnids, crustaceans, and (you knew this was coming :mrgreen:) cephs? Do they sleep, or have a biological process similar to sleep?

And if any of the above inverts do sleep.... do they dream? For that matter, do birds, reptiles, amphibians, and fish dream? Everyone here has seen a dog or cat wildly chasing imaginary prey in dreamland, but I don't know how one would measure REM sleep in non-mammalian species.

Maybe this could best be summarized by two basic questions:

1. At what point on the evolutionary ladder does the ability/necessity to sleep begin?

And, having determined that....

2. Among those species which do sleep, at what point on the evolutionary ladder does the ability/necessity of dreaming (as indicated by REM sleep, for want of a better criterion) begin?

This may sound silly, but I am genuinely curious about the whole thing..... which keeps me awake at night. Literally. Steve-O'? Kat? Monty? Nancy? Anybody?

:bugout:

Tani
 

OB

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I think this is as always an excellent question, my dearest and most benthic buddy.

To my understanding, the query is twofold:

1: To which extent does the complexity of the neural network as such give rise to "random firing" (for reasons of "chaos" organising itself through nominal feedback) in the rest state.

2: Does the ability of "memory" equate the possibility to dream?

Addendum: at which level of consciousness/self awareness do neural activities become "experiences" or "dreams"? I would say a lot earlier on in evolution than most would feel comfortable with from a classic man/nature division point of view.
 

monty

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I think this is a tough question, largely because we know so little about the evolutionary origins and purposes of sleep.

My completely wild guess is that sleep as we know it is an evolutionary quirk more than a necessity for a system to be a proper brain, so I would not be at all shocked if it happened to develop in an early vertebrate ancestor and became locked in, which would lead me to think it might not be present in invertebrates. However, maybe it, or a precursor that makes it inevitable, developed with the first nervous systems, and made any sufficiently complex brain require it in some form.

I can't see any reason why sleep would be mandatory, so my :twocents: is that it all depends on whether the precursor for sleep was present in our last common ancestor with cephs (a rather long time ago, likely Precambrian.)
 

robyn

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This is such a cool topic... I disagree with Monty slightly in that I don't think sleep or its analogue need be present in the common ancestor of cephs and mammals, but instead that 'sleep' is something that arises in concert with some minimum biological level of neural complexity. I'm not certain that it need be concurrent with an ability to form memories, but I agree that one purpose of dreaming is in reconsolidation and possibly extinction of memories.

As for cephs specifically, there is at least behavioural evidence of sleeping in octopuses (pupil contractions, reduced colour changes and lowered respiratory rates), and evidence that 'sleep deprivation' on one occasion results in rebound sleeping in the next sleep cycle. Which is very cool, but I agree that its a complete mystery still to ascribe a 'purpose' to sleeping in species as remote as molluscs and mammals.

So, in conclusion, I really have no idea. But its a great discussion topic. I hope more people will weigh in here.
 

Architeuthoceras

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Is "instinct" a form of dreaming? Did ammonoids dream of going to the spawning grounds? Do squid dream of going to the spawning grounds? Do turtles dream of going to a specific island at a certain time in their life? Surely they dont just end up where they need to be by chance, something tells them where to go. Could it possibly be dreams? I know I often dream of going to the spawning grounds, and I dont need to be sleeping. :wink:
 

monty

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robyn;127143 said:
This is such a cool topic... I disagree with Monty slightly in that I don't think sleep or its analogue need be present in the common ancestor of cephs and mammals, but instead that 'sleep' is something that arises in concert with some minimum biological level of neural complexity. I'm not certain that it need be concurrent with an ability to form memories, but I agree that one purpose of dreaming is in reconsolidation and possibly extinction of memories.

As for cephs specifically, there is at least behavioural evidence of sleeping in octopuses (pupil contractions, reduced colour changes and lowered respiratory rates), and evidence that 'sleep deprivation' on one occasion results in rebound sleeping in the next sleep cycle. Which is very cool, but I agree that its a complete mystery still to ascribe a 'purpose' to sleeping in species as remote as molluscs and mammals.

So, in conclusion, I really have no idea. But its a great discussion topic. I hope more people will weigh in here.

Hmm. I guess the real question is "is sleep something that's important to higher mental capabilities?"-- it sounds like you think it may be, while I'm not so sure. Computers don't need to sleep, but they don't exactly think, either.

One analogy is that a memory-related structure found in many (all?) vertebrates is the hippocampus, but in cephs, there is a rather different-looking vertical lobe system. Perhaps as we explore, we'll find that there are parallels between the two, perhaps even including a need for sleep, but it's also possible cephs have evolved a completely different system to address the same problems of memory and learning.

In the case of eyes, vertebrate and ceph eyes are quite similar, but arise from different germ layers (IIRC) and are "inside out" relative to one another. I think that's a sign that there are aspects of eyes (lenses, retinas, pupils) that are fundamental to any animal developing vision. Is the same true of sleep? I have no idea.

All I really meant was that there seem to be 3 possibilities,

1) cephs don't sleep (which appears to be ruled out somewhat)

2) cephs and humans sleeping is convergent evolution, and arose because of similar evolutionary needs once their intelligence rose to some level (this is how I read Robyn's post...)

3) some common ancestor had a primitive sleep precursor, and that favored the evolution of sleep in both groups (this is my earlier thinking.)

Do any other intelligent-ish animals sleep or not? Spiders sit idle for long periods, I'm not sure about stomatopods, and bees seem to be idle in hives sometimes... I don't know if any of those should count as "sleep," though.

We really need to find extraterrestrial life and see if it sleeps...
 

DWhatley

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Architeuthoceras;127148 said:
I know I often dream of going to the spawning grounds, and I dont need to be sleeping. :wink:

humm, a week in the mountains with an attractive student and you start relating to your more recent cavemen ancestors :roll:. Your statement does bring up a question as well. Is it necessary to sleep to dream or is being asleep part of the definition of a dream?

Is anyone aware of studies done regarding sleep and internal repair? I have always been under the impression that sleep allowed the body to be active internally to do all the housework where awake time used similar energies to mobilize the container. If there is any merit to that folk understanding then it would make sense that any organisim (as a group, not individually) that is daily battered from its environment (thinking octo arms specifically) and needed to regenerate parts (all those new cells!) would require sleep and the need would be encoded so that even if the environment was friendly, the need would still exist.
 

monty

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Aw, the funnest discussions are when there are unanswered questions that might be answerable with the right cleverness and perhaps some investigation.... stick around, 'cause "Adult Swim" is just late night on the cartoon network...
 

OB

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Einstein was working at a patent office when he rewrote physics, so indeed, stick around from outside of the box! I am inclined to stick with my initial argument that dreaming arises from a minimum level of complexity and the presence of memory. With the reasons for sleep, I am a lot less certain. It could simply be that energy conservation has an evolutionary benefit as a trait? The disturbing fact is, that sleep deprivation kills, so the conserved trait must be about a lot more than mere savings; it has become essential.
 

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