But a remarkable new study has revealed that something similar may happen in humans as well - every night.
The research used a combination of scalp EEG, and electrodes planted inside the brain, to record brain activity from 5 people undergoing surgery to help cure severe epilepsy. The subjects were then allowed to go to sleep for the night, while recording took place.
As expected, after falling asleep, the EEG showed delta wave activity - strong, slow waves of electrical activity (0.5 to 4 Hz) which are typical of deep, dreamless "slow wave sleep".
However, the electrodes inside the brain told a different story. While they recorded delta waves most of the time, they also showed that there were episodes, lasting from a few seconds to up to 2 minutes, in which the motor cortex suddenly went into "waking mode". Delta waves disappeared, and were replaced with fast, unpredictable activity.
This image shows one episode, lasting just 5 seconds. The hotter the color, the more activity in a particular frequency. The higher the band, the higher the frequency. This shows a clear burst of high frequency activity in the motor cortex. The other parts of the brain showed the opposite effect - even stronger slow wave activity - at the same time.Another area, the dorsolateral prefrontal cortex, also showed this phenomenon occasionally, but it was much less common than in the motor cortex.
There's a few caveats. These patients had severe epilepsy, and they were taking anti-convulsant drugs. This wouldn't obviously create the effects seen here, but we can't rule it out. Still, these results are intriguing.
They challenge the view of slow wave sleep as a "whole brain" phenomenon. We've known for a while that this isn't true of animals, and in people with certain sleep disorders, but this is first demonstration in healthy humans.
It may help to explain the mysterious fact that, although slow wave sleep is often referred to as "dreamless", there are consistent reports that people woken up from this phase of sleep do report dreaming (or at least thinking) about things.
While episodic arousal of the motor cortex probably wouldn't explain this per se, if the same thing happens in the visual cortex or other sensory areas, it might create dreams.
Nobili L, Ferrara M, Moroni F, De Gennaro L, Russo GL, Campus C, Cardinale F, & De Carli F (2011). Dissociated wake-like and sleep-like electro-cortical activity during sleep. NeuroImage PMID: 21718789
11 comments:
What's remarkable is the hubris that presumed that homo sapiens would be any different from any other mammal, or any vertebrate for that matter since birds do the same.
I blame religion. For millenia it socially imprinted us with the absurd idea humans where not animals but something else all together.
That social imprint prevents many of us to have any kind of objectivity in regard to our status in the animal kingdom.
So we blandly assume that nothing animals do we do and see it as surprising that we do anyway.
Never ceases to amaze me, that blind spot.
Clearly, "normal" humans don't do what most of the animals that appear to sleep with half of a brain at a time do, which is move about, monitor the environment, and function to some extent, 24 hours a day.
Even if there is bilateral asymmetry in brain waves during sleep, either in all humans or in atypical humans in exceptional conditions as here, they aren't up and about 24 hours a day, so the part of the brain that disconnects the REM dreaming brain from responding the dream world with motor function still appears to be applying on a global basis even if there is some vestigal bilateral assymetry in what happens there.
Clearly they do. Watch any mother sleeping and the baby starts to cry.
Evidently logically a part of the brain is completely aware of the circumstances. Just you aren't.
We are just a monkey on the back of the ape. We can steer it a bit, but if it decides to go right it goes right no matter how hard the monkey pulls on its ears.
Is religion not a natural manifestation since we are all only natural, and hence, apes?
Sure it's natural. We have a special module for that.
Excerpt:
There was once a mammal. It needed a lot of little bits of operating systems in order to let all components of its body function properly. Over time they became so numerous that it needed a system to coordinate the other bits . That system became so complex that it was capable to reprogram itself in order to be able to assimilate the ever increasing flow of information. It called itself: conscience.
Objectively impossible to determine if it exists, since conscience itself determines what are the criteria defining conscience.
That conscience, in an attempt to preprogram future acts of the body, starts tell a tale to itself.
A continuous flowchart enabling it by correlating previous events and by means of extrapolation to arrive at a predefined future action.
The conscience calls that tale: reality. Again objectively impossible to determine if it exists, the conscience stipulates what is reality. The one conscience determines the tale in which a supernatural being must exist a reality, the other determines it to be unreal.
In this one can distinguish two different main categories of belief:
The rest:
http://petrossa.wordpress.com/2010/04/16/the-brain-believes-do-you/
@petrossa
The asymmetry seen during dolphins' sleep is very different from anything in humans. This is unrelated to the fact that there is activity in the brain during sleep (in humans and in all animals). We have only known about dolphin's hemispheric asymmetry during sleep for less than 50 years. I don't think people were prompted to discover it by religion. Unless they were part of some dolphin-worshiping religion, why would you want to make dolphins seem more unique than they are?
We're not animals. Science is just not there yet to investigate the human condition.
@Anonymous
You've missed my point. I don't want to elevate dolphins but reduce the hubris.
Homo Sapiens isn't superior to anything except in it's own mind. It sets the criteria what is superiority, so that's a stacked deck if ever I've seen one.
The point isn't which part of the brain is active in which way, the point is that it is active beyond your control.
You are not your brain. You are a mere side effect of a vast dataflow. An artifact.
Your brain calls the shots, not you.
@veri
There is no such thing as 'human condition' outside of the human condition. A such it's a completely subjective abstract, with no intrinsic value.
Somewhere out there is a predator out there stalking a human walking about happily in it's magnificent human condition, thinking: mmm that' a nice meal.
Objective superiority is survival. Survival as a species.
And in that department we are totally inferior to even a jellyfish by 500.000.000 years.
Petrossa, I believe there is. How many physicists were slapped with "no such thing" by the world to be later proven? Have faith.
It's been shown that SWS helps to consolidate declarative memory, memory of facts and events. REM sleep, on the other hand, has been found to consolidate emotional and procedural types of memory. So it makes sense why we have more static thought-like dreams during SWS and more emotional (usually involving fear, flight/fight) and non-nonsensical dreams during REM.
Is our normal sleep behaviour natural/healthy at all or is it culturally forced and learned in childhood? I mean the expectation that you should sleep around 8 hours uninterupted between 10pm and 8am.
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