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. 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. 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
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. 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, 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 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. If you would like to comment on this video or anything else you have seen on Future, head over to our or message us on. Sleeping isб easily one of the best things in life. The idea of a soft, comfy bed and a nice pillow, coupled with soothing ambience, means the world to almost every Бsleep loverБ, including myself. Sleep is not just amazing; itБs also rather mysterious! I call it БmysteriousБ because there are far too many things that we still do not completely understand about sleeping. For example, we might have a number of hypotheses and Бeducated guessesБ, but we don t really know the exact reason why we fall asleep in the first place! ThatБs just one example, but sleep is also home to a number of rather interesting natural and biochemical processes that occur within the body. One of them is involuntary twitching, something that we are going to discuss in this article. You may have noticed that, as you are about to fall asleep, your body twitches involuntarily, for no particular reason. ItБs even easier to notice this when someone next to you is falling asleep (full disclosure: it might even creep you out a little bit at first! ). There areб quite a few reasons why people twitch during their sleep, but one of the most common kinds of twitching is known as a hypnic jerk. Hypnic jerks are sudden but brief contractions of one or more limbs or the whole body as a person begins to fall asleep or is already in a sleep stage. Also referred to as a hypnagogic jerk or sleep start, a hypnic jerk commonly causes people to awaken suddenly (for a moment or two). In purely physical terms, a hypnic jerk resembles a БjumpБ experienced by a person whoБs startled,б which is why it s accompanied by a falling sensation. If you really think about it, the sensation of falling while sleeping is sort of weird,б right? Not only that, but sleep starts are also associated with a quickened heartbeat, sudden sweating and sometimes a peculiar sensory feeling of shock or falling into the void. What causes hypnic jerks? According to the, there are many things that might be potential causes of hypnic jerks, including anxiety, stress,б excess caffeine and strenuous activities, but most hypnic jerks occur absolutely randomly in healthy individuals.
An interesting hypothesis regarding the cause of hypnic jerks delves into the idea of evolution. According to, a psychologist at the University of Colorado, a hypnic jerk could be an archaic reflex to the brain s misinterpreting the muscle relaxation accompanying the onset of sleep as a signal that the sleeping primate is falling out of a tree. Б Allow me toб explain this in simple terms: imagine an animal that sleeps high up in trees. ThatБs quite dangerous to begin with, isnБt it? As such, if the animal falls into a deep sleep, it could risk falling out of the tree and being seriously hurt, or possibly even die! Now, suppose some of these animals wake up with a sudden start when they feel that they are falling. They obviously wouldn t fall to their death, thanks to the fact that they are now awake andб can adjust to a safer position. Thus, animals that experience the hypnic jerk have a much higher chance of living longer than those who donБt experience it. As such, they are more likely to pass on their Бhypnic jerkБ genes to their offspring, who would also experience a hypnic jerk, and thus live longer. The cycle goes on and on, and voila! б That s evolution! Therefore, it sб often claimed that hypnic jerks in humans are actually a remnant of the time when our primate ancestors slept high on tree branches to protect themselves from wild beasts that lurked in the dark. Another hypothesis proposes that you experience hypnic jerks as you start entering sleep because your brain БthinksБ that you are actually dying (due to certain changes that occur within your body at that time, such as dipping body temperature etc. ). б As a result, your brain jolts your muscles to ensure that you donБt die! According to this hypothesis, when you sleep, part of your brain goes to sleep and starts dreaming, but it doesn t shut down the part that keeps you conscious and controls your motor functions. That sб why you experience sudden spasms when youБre beginning to sleep; it s even more common when you are overly tired. б when you sleep, part of your brain goes to sleep and starts dreaming, but it doesn t shut down the part that keeps you conscious and controls your motor functions. That sб why you experience sudden spasms