There is some recent research that some chemicals are flushed through the brain during sleep to remove byproducts. Why that can't happen without sleep is another interesting question.
> Why that can't happen without sleep is another interesting question.
I would guess that since sleep has been optimized by evolution for a long time, and evolution is so creative, that there are now countless dependencies on that time/phase separation.
But umbrella reasons probably include all of these:
1. To recognize unhealthy build of material for removal, you have to stall normal production. Otherwise production and removal would waste each other's efforts and pernicious build up would be undetectable.
2. Some cellular machinery may be used during normal and clean up operations, in different things. Evolution is great at reusing whatever is available.
3. Sleep involves coordinating many systems. Some subsystems might technically be capable of operating more flexibly, but coordinating all the systems together makes overall coordination simple, efficient and reliable.
4. Sleep isn't low energy behavior. Segmenting energy use between waking and sleeping maintains a lower metabolism envelope.
5. Dreaming is high level behavior. Can't high level think and dream at the same time.
6. Dreaming sensory free, motor free, operation is fundamentally at odds with normal active sensory and motor activity.
7. A billion random dependences on phase separation have accumulated over millennia, at the psychological, gene, epigenetic and chemical level, with no pre-ordaned rationale other than the separation was dependable for the other reasons given.
Intersting that octopuses, whose brains are an entirely separate "alien" evolutionary invention, also appear to dream. [0]
I wonder if this is heavily based on the fact that during sleep, all inputs are shut down. Like, you can't hear, you can't see, you can't feel, no smell, no taste. All senses to the outside world are off.
What is it about external inputs that makes the brain not be able to do it's sleep "duties"?
Is it that external inputs take up processing power that needs to be used during sleep instead?
But that's not true. The senses are not off as you wake up when light increases, when there is a loud sound or when there is a stron smell. In addition there are numerous examples that the sound of the alarm clock gets integrated into the dream, maybe as a telephone sound for example.
Because when we are awake our brains run "hot" producing chemical waste - evolving on a world experiencing predictable day and night cycles led to sleep - it is not like we could do anything without sunlight back then.
It was also dangerous to do anything i.r.o nocturnal predators.
I would guess that since sleep has been optimized by evolution for a long time, and evolution is so creative, that there are now countless dependencies on that time/phase separation.
But umbrella reasons probably include all of these:
1. To recognize unhealthy build of material for removal, you have to stall normal production. Otherwise production and removal would waste each other's efforts and pernicious build up would be undetectable.
2. Some cellular machinery may be used during normal and clean up operations, in different things. Evolution is great at reusing whatever is available.
3. Sleep involves coordinating many systems. Some subsystems might technically be capable of operating more flexibly, but coordinating all the systems together makes overall coordination simple, efficient and reliable.
4. Sleep isn't low energy behavior. Segmenting energy use between waking and sleeping maintains a lower metabolism envelope.
5. Dreaming is high level behavior. Can't high level think and dream at the same time.
6. Dreaming sensory free, motor free, operation is fundamentally at odds with normal active sensory and motor activity.
7. A billion random dependences on phase separation have accumulated over millennia, at the psychological, gene, epigenetic and chemical level, with no pre-ordaned rationale other than the separation was dependable for the other reasons given.
Intersting that octopuses, whose brains are an entirely separate "alien" evolutionary invention, also appear to dream. [0]
[0] https://www.smithsonianmag.com/smart-news/octopuses-may-have...