Why your body jerks before you fall asleep

[Evil Eye]

As we give up our bodies to sleep, sudden twitches escape our brains, causing our arms and legs to jerk. Some people are startled by them, others are embarrassed. Me, I am fascinated by these twitches, known as hypnic jerks. Nobody knows for sure what causes them, but to me they represent the side effects of a hidden battle for control in the brain that happens each night on the cusp between wakefulness and dreams.



Normally we are paralysed while we sleep. Even during the most vivid dreams our muscles stay relaxed and still, showing little sign of our internal excitement. Events in the outside world usually get ignored: not that I’d recommend doing this but experiments have shown that even if you sleep with your eyes taped open and someone flashes a light at you it is unlikely that it will affect your dreams.



But the door between the dreamer and the outside world is not completely closed. Two kinds of movements escape the dreaming brain, and they each have a different story to tell.



Brain battle



The most common movements we make while asleep are rapid eye-movements. When we dream, our eyes move according to what we are dreaming about. If, for example, we dream we are watching a game of tennis our eyes will move from left to right with each volley. These movements generated in the dream world escape from normal sleep paralysis and leak into the real world. Seeing a sleeping persons' eyes move is the strongest sign that they are dreaming.



Hypnic jerks aren't like this. They are most common in children, when our dreams are most simple and they do not reflect what is happening in the dream world - if you dream of riding a bike you do not move your legs in circles. Instead, hypnic jerks seem to be a sign that the motor system can still exert some control over the body as sleep paralysis begins to take over. Rather than having a single “sleep-wake” switch in the brain for controlling our sleep (i.e. ON at night, OFF during the day), we have two opposing systems balanced against each other that go through a daily dance, where each has to wrest control from the other.



Deep in the brain, below the cortex (the most evolved part of the human brain) lies one of them: a network of nerve cells called the reticular activating system. This is nestled among the parts of the brain that govern basic physiological processes, such as breathing. When the reticular activating system is in full force we feel alert and restless - that is, we are awake.



Opposing this system is the ventrolateral preoptic nucleus: 'ventrolateral' means it is on the underside and towards the edge in the brain, 'preoptic' means it is just before the point where the nerves from the eyes cross. We call it the VLPO. The VLPO drives sleepiness, and its location near the optic nerve is presumably so that it can collect information about the beginning and end of daylight hours, and so influence our sleep cycles.



As the mind gives in to its normal task of interpreting the external world, and starts to generate its own entertainment, the struggle between the reticular activating system and VLPO tilts in favour of the latter. Sleep paralysis sets in. What happens next is not fully clear, but it seems that part of the story is that the struggle for control of the motor system is not quite over yet. Few battles are won completely in a single moment. As sleep paralysis sets in remaining daytime energy kindles and bursts out in seemingly random movements. In other words, hypnic jerks are the last gasps of normal daytime motor control.



Some people report that hypnic jerks happen as they dream they are falling or tripping up. This is an example of the rare phenomenon known as dream incorporation, where something external, such as an alarm clock, is built into your dreams. When this does happen, it illustrates our mind's amazing capacity to generate plausible stories. In dreams, the planning and foresight areas of the brain are suppressed, allowing the mind to react creatively to wherever it wanders - much like a jazz improviser responds to fellow musicians to inspire what they play.



As hypnic jerks escape during the struggle between wake and sleep, the mind is undergoing its own transition. In the waking world we must make sense of external events. In dreams the mind tries to make sense of its own activity, resulting in dreams. Whilst a veil is drawn over most of the external world as we fall asleep, hypnic jerks are obviously close enough to home - being movements of our own bodies - to attract the attention of sleeping consciousness. Along with the hallucinated night-time world they get incorporated into our dreams.



So there is a pleasing symmetry between the two kinds of movements we make when asleep. Rapid eye movements are the traces of dreams that can be seen in the waking world. Hypnic jerks seem to be the traces of waking life that intrude on the dream world.

Source: http://www.bbc.com/future/story/20120522-suffer-from-sleep-shudders





Apparently sleep paralysis is very scary (while still conscious obviously)... Anyone ever experienced it?

 

[DrLeftover]

I just thought it was the demons from under the bed coming to get you.

 

[Evil Eye]

I just thought it was the demons from under the bed coming to get you.

Well, I don't have any demons under my bed, but I suppose that might be different for some people...

 

[Raven]

I have woken up a few times and been unable to move. I wanted to move my legs or arms to get up and I psychically could not move. When I tell people, they say I was dreaming, but I wasn't, I had woken up! Very very scarey feeling.



I sometimes have the odd jerk of the head or leg when I am laying in bed, but I've always put that down to my tremor.



I'm also sometimes aware of me moving... or singing in my sleep, sometimes it wakes me up. If I am asleep on the sofa and the tele is on, I can still hear the tv in my dreams, and if an alarm or something is going off then I dream about an alarm going off in my dream.... weird.



EDIT: Reading further on it says about the alarm clock.... so i'm not so weird after all!

 

[DrLeftover]

[font=courier new,courier,monospace]Tonight,​

[font=courier new,courier,monospace]is a Good Night,​

[font=courier new,courier,monospace]to Wake Up​

[font=courier new,courier,monospace]SCREAMING.​

 

[DrLeftover]

Not only does it exist. It is one of the more fascinating facets of the human condition.



http://www.webmd.com/sleep-disorders/guide/sleep-paralysis



hang on... I need a fix of Metalica's Enter Sandman



Should I post it here?



http://www.youtube.com/watch?v=1QP-SIW6iKY



No?



Sorry

 

[Evil Eye]

You're not even remotely sorry

EDIT: Reading further on it says about the alarm clock.... so i'm not so weird after all!

Yay!

Not only does it exist. It is one of the more fascinating facets of the human condition.

Indeed and as everyone keeps confirming, very scary.

 

[Raven]

Why is it then, that so many people toss and turn? I suppose that is before they reach REM sleep? Strange...

I don't think people have reached the dream state when they toss and turn. For me when I turn over I wake myself up. When I toss and turn at night it is because I am stressed and that stops me from sleeping properly.



Just found this, Another interesting article http://www.thefreelibrary.com/What+Really+Happens+while+We+Sleep?-a01073990860