Pseudo-Psychology Claims: Sleep twitching occurs because the brain mistakenly believes the body is dying, triggering a pulse. Science Explains: Sleep twitching may result from the brain processing information. Here's how it all began...
A Weibo account calling itself "Classic Psychology" shared this anecdote: Have you ever suddenly kicked your leg or twitched while sleeping? Here's the truth—it's called a muscle twitch, commonly occurring during sleep. When breathing slows too much, the brain perceives the body as nearing death, so it sends a pulse to wake you up.People who frequently experience muscle twitches should take note—it indicates your body's functions aren't in top shape.
Undoubtedly, this statement carries an alarmist tone. If myotonia frequently occurs during sleep and suggests poor health in those who experience it, doesn't that imply many people are unhealthy? This phrasing is indeed overly vague.
First, let's clarify what myotonia is. It refers to rapid, involuntary muscle contractions resembling an electric shock.While severe myoclonus can be a physical disorder affecting daily life, physiological muscle jerks—such as hiccups, hypnic jerks, or twitches from fatigue or tension—are common in healthy individuals and generally unrelated to overall health.
So, is that sudden jerking kick during sleep actually a muscle twitch?
Hypnic Jerk
Academically, that sudden kicking motion during sleep is termed a "hypnic jerk" (or hypnagogic jerk).Many folk beliefs attribute this jerking to growth spurts, but this claim is entirely unfounded. Have you ever heard of Yao Ming kicking down walls as a child?
Hypnic jerks refer to sudden, involuntary muscle contractions occurring just as one is falling asleep.This process is often accompanied by a sensation of free-falling or even vague dreams, and may cause sudden awakening. While typical hypnic jerks do not disrupt sleep, excessive frequency can lead to periodic limb movement disorder (PLMD), transforming individuals into "jerking men" or "jerking women" and causing insomnia.
The causes of this phenomenon remain debated. One theory suggests that as individuals transition from wakefulness to sleep, their heart rate slows, body temperature drops, breathing becomes more relaxed, and muscles gradually relax. The reticular activating system (RAS) governs this transition process, and sleep startles may simply be a side effect arising when the RAS misinterprets data.
Another intriguing explanation suggests that the human brain evolved from reptilian brain structures, retaining some reptilian stress response patterns. When muscles fully relax, the brain may interpret this as free-falling based on these stress response patterns. To protect itself, the brain commands the entire musculature to act immediately, attempting to grasp something during the fall.Thus, previously relaxed muscles suddenly contract, triggering sleep jerks.
Muscle Twitches
In fact, besides the well-known "sleep jerks," "sleep spindles" occurring during stage 2 slow-wave sleep may also cause "muscle twitches."
Sleep spindles are specialized brain waves commonly found in the thalamus and cerebral cortex. They manifest as sudden, intense oscillations in brain waves, often accompanied by brief, localized muscle twitches.
Muscle twitches during sleep are more common in infants.Researchers believe this represents the brain learning or consolidating neural-muscular correspondences, a process facilitated by undisturbed sleep. This explanation sheds light on why infants appear to sleep constantly—they are diligently engaging in "twitch sleep learning."Additional research indicates that sleep spindles do indeed aid in integrating new information with existing knowledge, offering further support for the "spike-and-wave sleep learning" hypothesis.
Moreover, sleep spindles help maintain restful sleep. The frequency of brainwave activity in the thalamus correlates with the ability to sustain calm sleep, and spindles originating in the thalamus can act as a shield against sudden external auditory stimuli.A study from Harvard Medical School's Division of Sleep Medicine indicates that the higher the frequency of sleep spindles in EEG waves, the stronger an individual's ability to resist external disturbances and maintain sleep, resulting in better sleep quality.
Jerking vs. Trembling
On the surface, "sleep jerks" and "muscle tremors" appear to have different causes and purposes, yet both seem to result in sudden muscle contractions. So what distinguishes their outward manifestations?
We can identify them through two aspects.
First, the pattern of twitching differs. While the exact cause of sleep startles remains unclear—whether due to a glitch in the reticular activating system or the brain's illusion of falling—the resulting "twitching pattern" is always whole-body. Sleep startles are often vividly described as "an electric shock-like tremor throughout the body."Second, sleep spindles induce muscle tremors to learn or consolidate muscle control, making localized twitching more common.Just as a puppeteer learning to manipulate a puppet must progress step by step—after all, taking too big a step can easily lead to a fall.
On the other hand, the outcomes of the jerks differ. First, during sleep jerks, the individual is not fully asleep; the whole-body jerk often jolts them awake. When muscles are fatigued or sleep is lacking, the jerks tend to be more severe.The more you need sleep, the more your body twitches uncontrollably. Don't worry—you've merely been woken during the first sleep stage, which isn't a big loss. Just stay calm and try again; in ten minutes, you'll be back to being a sleep god! Secondly, sleep spindles occur during sleep itself and serve a protective function.So it's quite possible you twitched for ages without waking yourself, but ended up startling the person sleeping next to you...
Quick Quiz
In a pitch-black night, a young man had just finished browsing the latest article on Guokr.com. He then decided to shut down his computer and go to sleep, lying down in bed with an atmosphere both peaceful and solemn.Just when everyone thought he was asleep, suddenly this fellow's body jerked violently, startling you beside him.
The question arises: Was this twitch caused by sleep startle or muscle tremors from the Sleep Pill?
The self-check method is simple: immediately ask the young man a question: "Did you twitch?"
If he can answer you clearly, it's a "sleep startle"; if he's too deep to respond, it's the "sleep pill" effect—his brain is learning.
PS: The first third of sleep is slow-wave sleep, considered deep sleep. During this phase, EEG waves show the classic pattern of deep slumber.