When we give up our bodies to sleep, sudden twitches escape our brains and cause our arms and legs to jerk. Some people are startled by them, while others are embarrassed. These twitches, known as hypnic jerks, are fascinating to me.
It’s not clear what causes these twitches, but they are side effects of a hidden battle for control in the brain on the verge between wakefulness and dreams. We usually are not able to move while we sleep.
During the most vivid dreams, our muscles remain relaxed and still, showing little sign of our excitement. Studies show that even if you sleep with your eyes taped open, and someone flashes a light at you, it will not likely affect your dreams.
The borderline between the dreamer and the outside world isn’t completely closed. Two different movements escape the dreaming brain, each with a different story to tell.
Brain Battle: The Possible Reasons
Rapid eye movements are one of the most common movements we make while asleep. When we dream, our eyes move based on our dreams. If we were to dream that we were watching a tennis game, our eyes would move from left to right with each volley.
The movements generated in the dream world escape from normal sleep paralysis and make their way into the real world. The most vital sign that a person dreams is when the eyes move.
If you dream of riding a bike but don’t move your legs in circles, you don’t reflect on what is happening in the dream world.
As sleep paralysis starts to take over, hypnic jerks seem to be a sign that the motor system can still take control over the body. We don’t need a single sleep-wake switch in the brain to control our sleep. Instead, we have two systems balanced against each other that go through a daily dance, where they have to wrest control from each other.
Beneath the cortex, deep in the brain, is the reticular activating system. It’s one of the most critical networks in the human brain. Located near the midbrain, the locus coeruleus helps regulate essential bodily functions like breathing.
When the reticular activating system is activated, we feel attentive and restless; that is, we are awake. The opposing system is the ventral pre-mammillary nucleus, situated near the ventral border of the third ventricle. It controls the ventrolateral part of the hypothalamus.
When we need to do something at night, it seems to use a mechanism called the VLPO to help us fall asleep. It seems to gather information about when daylight begins and ends and is located near the optic nerve.
As the mind gives in to its regular activity of interpreting the external world and generating its entertainment, the struggle between the reticular activated system and the VLPO tilts in favor of the latter. Lack of sleep causes sleep paralysis. Part of the story is that the struggle for control of the motor system is not over yet, even though what happens next is not fully clear. Few battles are complete in a single moment.
As sleep paralysis sets in, daytime energy suddenly rises and falls in seemingly random movements. As such, hypnic jerks are the last gasps of daytime motor control.
Some people say they experience hypnic jerks when they dream they are falling or tripping up. This is an example of a rare phenomenon called dream inclusion, where an alarm clock is built into your dreams.
Our mind’s ability to generate plausible stories is demonstrated when this does happen. In dreams, planning and foresight areas of the brain are repressed, allowing the mind to react creatively to wherever it wanders – much like a jazz improviser responds to fellow musicians to inspire what they play.
The mind is transitioning as hypnic jerks escape between wake and sleep. Therefore, we must understand external events in the waking world.
The brain tries to make sense of its activity in dreams. Hypnic jerks are movements of our bodies that attract the attention of sleeping consciousness because they are close to home.
Along with the nighttime world, they get incorporated into our dreams. There is a symmetry between the movements we make when we are asleep. In the waking world, rapid eye movements can be seen in dreams. There seem to be traces of waking life in the dream world.