Unqualified anonymous internet answer: it's probably too busy.
I believe the brain actually shrinks slightly and channels expand to aid in the flushing.
Anectdata: note how when you're really tired you can't think clearly? Also, how (apparently) if one goes without sleep for too long then the brain suffers irreparable damage.
>Cassiopea has no brain to speak of — just a diffuse “net” of nerve cells distributed across their small, squishy bodies. These jellyfish barely even behave like animals. Instead of mouths, they suck in food through pores in their tentacles. They also get energy via a symbiotic relationship with tiny photosynthetic organisms that live inside their cells. //
From a very cursory glance I can't see how they're differentiating low energy level from lack of "sleep" when they're keeping the jellies "awake". Can that behaviour (resting more the next day) just be explained by low energy reserves, and the jellies needing more time to glean energy from the photosynthesising organisms/cells?
Don't plants in winter "sleep" according to their definition; they can wake with a "false spring".
Moderators: the title should be changed to the actual article title, which is:
"Scientists just discovered the first brainless animal that sleeps"
The submitted title, "Scientists just discovered the first animal without a brain that sleeps", is ambiguous. In addition to the correct meaning, it could also have meant the first animal whoe brain does not sleep.
1. It is not known whether or not pelagic fish sleep. They do not show any of the external signs that are used to infer sleep in other species.
Many scientists believe that to solidify and organize memory and learning the brain needs a period with little or no environmental distractions, and that the purpose of sleep is to provide such a period.
Pelagic fish live in an environment with such a sparse environment that their brains may be able to do that processing without disconnecting and so do not need to sleep.
This means it is plausible that there are animals with brains whose brains do not sleep. If such an animal is shown to exist, it will be the first such case, and so a headline saying that the first animal with a brain where the brain does not sleep is a plausible headline.
2. There are a variety of externally observable behaviors of animals that indicate that the sleeping (especially when "externally observable" includes "observable when hooked up to a variety of instruments").
Not all of these are associated with functions that require a brain. Hence, it is plausible that there is a brainless animal that exhibits some of these sleep-associated behaviors, perhaps even enough of them that it would make sense to say they sleep, even though they have no brain.
Hence, a headline saying the first animal that does not have a brain yet sleeps has been found is plausible.
If we have to decide that one of these interpretations is the one people would expect by "common sense", I would argue that it is the first one. Yes, I realize that most people will not know about our uncertainty over the sleep or lack of sleep in pelagic fish, so would not come to the first interpretation by that route.
However, most people's experience with sleep is based on their first hand knowledge from doing it themselves almost every day, and from talking to other people who do it, and from observing it in fairly intelligent animals such as dogs and cats. They are going to think of sleep as a cognitive thing, something that only animals with brains can do. Since they will have dismissed sleep without a brain as not even possible, they would go for the other interpretation--a brain that does not sleep.
So even if we conclude that the submitted title really only has one "common sense" reading, that reading is the wrong one, so the headline is still a bad headline and should be changed.
I wish we could replicate this in humans (for testing purposes). What personality, intelligence and creativity differences would there be between full and 1/2 left and 1/2 right being asleep? Would it be the same for everyone, or have some people adjusted so that each 1/2 brain is effectively just a smaller (but "fully functioning") brain?
Yeah, my first thought was the latter interpretation. Got excited for a moment that we may someday be able to cure sleep (kidding, of course -- sleep is glorious).
People talk about all the amazing ways we'll one day be able to put technology in our brains. Things like having immediate access to all accumulated human knowledge, etc. I just want to be able to program my brain to perfectly regulate my sleep such that I wake up exactly when I want perfectly refreshed. You can have instant trivia, give me perfect sleep.
Not an expert on jellyfish physiology, but might there be a distinction between "a sleep-like state" and being plain "tired"? After doing some physical activity animals tend to need some rest. Exhaustion is much less of an exciting phenomenon than sleep is.
Induced exhaustion is one way to test it, yes. Can't say from the article if they ruled it out. Correlation of the rest pattern with a day-night cycle does not necessarily imply that the "sleep-like" state is indeed sleep, and not just a power-down low-metabolical wait-state used for the bio-chemistry to catch up after a day of activity is over.
Sleep is typically defined by the brain waves activities, delta waves, theta waves, etc., each corresponding to a specific sleep stage. These are physiological markers of sleep. There are also states of "quiet wakefulness" that share behavioral characteristics of sleep, like immobility, for example, but are not sleep per se.
Many "simple animals" like a fly, or a caterpillar or a bee have periods of inactivity that could be an example of rest. But sleep and rest are not the same. If we put brain waves aside, we are left with the behavioral definition of sleep: it is a state of reduced awareness of the surroundings, there will be some latency in arousal, it is reversable, and it is associated either with immobility or at least reduced activity. This study obviously used this definition, so it is not exactly being "tired".
Thank you for articulating the difference between the two. Can it not be the case with exhaustion also, that awareness and/or reaction times are reduced? Cognition certainly is affected after strain in higher order animals and muscle cells need to replenish ATP.
Removing brain waves from the equation, it seems like the whole question of what attests for sleep gets blurry.
Sleep is not just "reduced" cognition, it is an entirely different state all together. In sleep thalamus becomes a gatekeeper that makes sure that stimuli cannot get through (although the important ones still do, like a baby cry will nearly always awaken a mother, even a faint cry will do). So, again, it is more radical than "quiet wakefulness" due to exhaustion.
Now, with "lower" animals it gets tricky, because all we have is a behavioral definition of sleep. But still, it makes a distinction of reduced awareness, arousal latency. Can we call it "sleep" in these animals, jellies included? Maybe not, maybe it is some sort of proto-sleep state?
Yes, it's getting interesting. There are probably significant differences in chemical activity in cells that could be quantified and strictly detect in which state the organism is in.
I'm not convinced because your answer doesn't address the nervous activity of these lower animals. Maybe they don't exhibit any at all in that state, but there's no reason to preclude this diffuse, sparse network from exhibiting patterns exhibiting precursors to sleep comparable to at least one of the human sleep phases.
spoiler: it's merely the avatar of a 4th dimensional eldritch horror and is actually studying the scientists before treating our realm as a cheap buffet.
In my humble opinion every animal consistent of multiple cells alive on this planet developed sleep for just one reason: the very same reason plants sleep. Our planet has a night phase and without sun little energy is left. So as a consequence the best one can do is to clean up internal processes or go into some sort of energy saving mode. Ofc this is heretic to some individuals...
_probably_ right. Wikipedia: "Since one can always burden failing explanations with ad hoc hypotheses to prevent them from being falsified, simpler theories are preferable to more complex ones because they are more testable." [1]
And this is easily testable. We just house a population of animals who sleep in a hermetically sealed environment that provides all that they need, but is never in darkness. After a couple of hundred million years we open the door and see if anyone is napping.
Not even "probably" right. Eg Quantum Physics is more complex than Newtonian. OcRaz is a heuristic that advises that simpler hypotheses should be tested first. It's not a magic SCIENCE! gun.
Occams Razor, often misused as you imply, says not to multiply elements beyond necessity. Newtonian physics doesn't explain observed quantum effects and so there is a necessity to use a more complex system to explain all the observations.
You're quite right to note it's heuristic nature, some people use it as if it's truth generating.
Seriously though, the existence of nocturnal animals kinda puts that argument to bed. While there might be selection pressure to specialise within day or night cycles, it's simply not plausible that no animal, in the vastness of the biospehere, has not generalised to do both, without some critical and fundamental flaw.
there might be a differential equation that describes a small part of beings (not a "huge number") benefitting from the free energy that diurnal animals might be at night. There's an equilibrium that's clearly preferential to daylight animals.
Point in case, bats as my primary example seem to be pretty archaic, with highly developed specializations, but nothing really highly developed. Which I see as an expression of the low entropy in the dark (the signal to noise ratio for sound is rather good at night though). Deep see animals are mostly outliers inhabiting a niche, as well. Whereas people as the highest developed species, if I may say so myself, don't even quite get along with crossing the day-night boundaries, I don't see your argument at all. You are rather proving the point.
So what this may be telling us is that sleep is required for beings with nerve cells, rather than solely for those with concentrated and clearly defined brains. This would make sense. All animals with brains sleep, but diversity of brain configuration and design exhibited across all of these different animal species would indicate that there's no single aspect of a brain that demands sleep, and therefore sleep is not an emergent property of collections of neurons forming brains but something the neurons themselves demand in order to function.
Possible. Or it could just be light as a confounding signal -- they get energy from it, after all, and animals with brains and eyes will spend energy more efficiently during the day.
Well I was thinking that light could impact the availability of their food source and so what the researchers interpret as sleep is just some other form of energy conservation, but the 'groggy' behavior of the jellyfish in their one experiment made me think that their energy conserving state does involve their neurons and so at that point it's hard to distinguish energy conservation from sleep.
I'm not trying to be snarky (in case it sounds like it):
But I thought that was the obvious part? Brains are made of neurons and (I thought) neurons produce biproducts that have to be "cleaned up" or they slow down/stop working. Isn't that also why (or one possible reason they think why) people with Alzheimer lose their brains? That it was somehow related to the brain's neuron "clean up" helpers that stop working or die off.
Then again, the less obvious thing is that the spinal cord has neurons. So I wonder if this comes into play there...
What is even more interesting is why exactly do they "sleep" at night? Do they have some sort of circadian rhythm? They are filter feeders, so the time of the day should not be that important, after all they can filter feed at night? Maybe it is a byproduct of being in lab? Since they are fed during the daytime, they might have "adjusted" to the lab schedule? They need light though, for their photosynthesizing symbionts.
(Aside: that first link, from 2014, already states that box jellyfish sleep, so this doesn’t seem to be as new as this article claims it to be. What (I guesstimate) is new is that they did pharmacological work to show that the jellyfish didn’t simply ‘not move’)
Somewhere I've heard a cool idea that sleep might be the "default" state of the living organisms. Most of the time you want to rest and conserve energy, so sleeping is just how we are, it's waking up to get food and procreate is the "strange" thing we do.
No idea if this makes sense scientifically, but it's fun to think about.
Or maybe animals that walk around during the time when there's no light just get themselves into trouble more often and end up dying out of the gene pool. Might as well shut down during the dangerous time and use it for repair.
The only issue with this idea is that it really ... doesn't tie in with evolution. Because ultimately, the default state of any organism should be to be attempting to reproduce. But I stress "ultimately", because there's nothing which impels us to think that needs to be the case at all times. Idling can be a successful short-term strategy, even if not in perpetuity.
A follow-up question I'd like to see researched is jet lag. Why do the jellyfish sleep during those hours? Can they adjust their circadian rhythm to a different time zone?
63 comments
[ 2.1 ms ] story [ 39.6 ms ] threadHere's to hoping this research helps is discover why we evolved to sleep.
I believe the brain actually shrinks slightly and channels expand to aid in the flushing.
Anectdata: note how when you're really tired you can't think clearly? Also, how (apparently) if one goes without sleep for too long then the brain suffers irreparable damage.
>Cassiopea has no brain to speak of — just a diffuse “net” of nerve cells distributed across their small, squishy bodies. These jellyfish barely even behave like animals. Instead of mouths, they suck in food through pores in their tentacles. They also get energy via a symbiotic relationship with tiny photosynthetic organisms that live inside their cells. //
From a very cursory glance I can't see how they're differentiating low energy level from lack of "sleep" when they're keeping the jellies "awake". Can that behaviour (resting more the next day) just be explained by low energy reserves, and the jellies needing more time to glean energy from the photosynthesising organisms/cells?
Don't plants in winter "sleep" according to their definition; they can wake with a "false spring".
"Scientists just discovered the first brainless animal that sleeps"
The submitted title, "Scientists just discovered the first animal without a brain that sleeps", is ambiguous. In addition to the correct meaning, it could also have meant the first animal whoe brain does not sleep.
Are there animals who don’t sleep but whose brains sleep?
While ambiguous from a purely grammatical point of view, it does not seem ambiguous from a “common sense” point of view.
https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
Many scientists believe that to solidify and organize memory and learning the brain needs a period with little or no environmental distractions, and that the purpose of sleep is to provide such a period.
Pelagic fish live in an environment with such a sparse environment that their brains may be able to do that processing without disconnecting and so do not need to sleep.
This means it is plausible that there are animals with brains whose brains do not sleep. If such an animal is shown to exist, it will be the first such case, and so a headline saying that the first animal with a brain where the brain does not sleep is a plausible headline.
2. There are a variety of externally observable behaviors of animals that indicate that the sleeping (especially when "externally observable" includes "observable when hooked up to a variety of instruments").
Not all of these are associated with functions that require a brain. Hence, it is plausible that there is a brainless animal that exhibits some of these sleep-associated behaviors, perhaps even enough of them that it would make sense to say they sleep, even though they have no brain.
Hence, a headline saying the first animal that does not have a brain yet sleeps has been found is plausible.
If we have to decide that one of these interpretations is the one people would expect by "common sense", I would argue that it is the first one. Yes, I realize that most people will not know about our uncertainty over the sleep or lack of sleep in pelagic fish, so would not come to the first interpretation by that route.
However, most people's experience with sleep is based on their first hand knowledge from doing it themselves almost every day, and from talking to other people who do it, and from observing it in fairly intelligent animals such as dogs and cats. They are going to think of sleep as a cognitive thing, something that only animals with brains can do. Since they will have dismissed sleep without a brain as not even possible, they would go for the other interpretation--a brain that does not sleep.
So even if we conclude that the submitted title really only has one "common sense" reading, that reading is the wrong one, so the headline is still a bad headline and should be changed.
Very interesting topic.
Many "simple animals" like a fly, or a caterpillar or a bee have periods of inactivity that could be an example of rest. But sleep and rest are not the same. If we put brain waves aside, we are left with the behavioral definition of sleep: it is a state of reduced awareness of the surroundings, there will be some latency in arousal, it is reversable, and it is associated either with immobility or at least reduced activity. This study obviously used this definition, so it is not exactly being "tired".
Removing brain waves from the equation, it seems like the whole question of what attests for sleep gets blurry.
Now, with "lower" animals it gets tricky, because all we have is a behavioral definition of sleep. But still, it makes a distinction of reduced awareness, arousal latency. Can we call it "sleep" in these animals, jellies included? Maybe not, maybe it is some sort of proto-sleep state?
But Ockham's razor tells me I'm right.
_probably_ right. Wikipedia: "Since one can always burden failing explanations with ad hoc hypotheses to prevent them from being falsified, simpler theories are preferable to more complex ones because they are more testable." [1]
[1] https://en.wikipedia.org/wiki/Occam%27s_razor
You're quite right to note it's heuristic nature, some people use it as if it's truth generating.
This doesn't explain the huge number of nocturnal animals that sleep during the day and are active at night.
Seriously though, the existence of nocturnal animals kinda puts that argument to bed. While there might be selection pressure to specialise within day or night cycles, it's simply not plausible that no animal, in the vastness of the biospehere, has not generalised to do both, without some critical and fundamental flaw.
Point in case, bats as my primary example seem to be pretty archaic, with highly developed specializations, but nothing really highly developed. Which I see as an expression of the low entropy in the dark (the signal to noise ratio for sound is rather good at night though). Deep see animals are mostly outliers inhabiting a niche, as well. Whereas people as the highest developed species, if I may say so myself, don't even quite get along with crossing the day-night boundaries, I don't see your argument at all. You are rather proving the point.
Predators which hunt at night occured later (another heretic thought).
I'm curious why you keep presenting your opinions as extreme outliers when they aren't particularly outside mainstream scientific thought?
A much older article on jellyfish sleep suggests this proposed advantage, at least: https://search.proquest.com/openview/c958b584511e462a64623c5...
But I thought that was the obvious part? Brains are made of neurons and (I thought) neurons produce biproducts that have to be "cleaned up" or they slow down/stop working. Isn't that also why (or one possible reason they think why) people with Alzheimer lose their brains? That it was somehow related to the brain's neuron "clean up" helpers that stop working or die off.
Then again, the less obvious thing is that the spinal cord has neurons. So I wonder if this comes into play there...
It's too bad that this seems to be the environment that our up-and-coming generation of scientists operate in.
(Aside: that first link, from 2014, already states that box jellyfish sleep, so this doesn’t seem to be as new as this article claims it to be. What (I guesstimate) is new is that they did pharmacological work to show that the jellyfish didn’t simply ‘not move’)
No idea if this makes sense scientifically, but it's fun to think about.
Or maybe animals that walk around during the time when there's no light just get themselves into trouble more often and end up dying out of the gene pool. Might as well shut down during the dangerous time and use it for repair.
A follow-up question I'd like to see researched is jet lag. Why do the jellyfish sleep during those hours? Can they adjust their circadian rhythm to a different time zone?