YoImagine waking up in the middle of the night and starting to drive your car around town or preparing a big bowl of dog food and eating it—and though your eyes are wide open, you are fast asleep. While these experiences sound like fiction, they are examples of a curious condition that occurs on the brink of sleep, known as “sleepwalking.” Sleepwalking is the so-called “arousal disorder”, a form of partial awakening during sleep, which affects around 2.5% of adults and as many as 14% of children. And it is this strange phenomenon that not only gives us insight into how dissociative mechanisms occur during sleep and how they can break down, but also provides clues into the nature of consciousness itself.
Each night, you go through 90-minute sleep cycles, moving through unique stages. During “light sleep” (known as Stages 1 and 2), your heart rate and body temperature drop, a sort of transition phase between wakefulness and sleep. But it’s in “deep sleep” (Stage 3) that your brain engages in critical cleansing tasks for your body. These include the release of hormones to repair your skin, replenish your cardiovascular and immune systems, and create new memories. During this time, your neurons literally shrink allowing cerebrospinal fluid to bathe your brain and rid it of harmful toxins. Deep sleep is a form of restful sleep, and it is often difficult to wake up the sleeper. The fourth stage, called rapid eye movement sleep, or “REM” sleep for short, is called “paradoxical sleep.” And for good reason: Blood pressure, heartbeat, and breathing speed up, and brain waves speed up. If we eavesdrop on the activity of neurons during REM, resemble those of wakefulness. We have our sharpest, most realistic and emotional dreams during REM sleep. To prevent you from acting out these REM dreams and injuring yourself, your brain temporarily paralyzes your entire body. This transition is tightly controlled by chemicals released from the bottom of the brain that tip the brain between sleep and wakefulness.
Read more: Why sleep paralysis makes you see ghosts
Sleepwalking does not occur during REM sleep but during deep sleep, dispelling the common myth that the sleepwalker is a confused dreamer who wanders around the house enacting strange dreams. This is practically never the case. Unsurprisingly, sleepwalking is most common in the early part of the night, when deep sleep is abundant.
Unlike REM, the activity of the cortex during deep sleep, which is located in the outer layer of the brain, almost like a motorcycle helmet, slows down enormously. But this architecture of deep sleep can sometimes inadvertently collapse: arousal of the brain’s emotional headquarters, the so-called “limbic system,” can become hyperactive and tickle the cortex that rests on it, causing partially wake the person. deep sleep In fact, this activation causes the brain to be awake and asleep at the same time, as if the world of sleep and wakefulness collided.
Neural neighborhoods important for logical thinking and self-awareness, such as the dorsolateral prefrontal cortex (strips of cell tissue on the front sides of both brain hemispheres) lie dormant while areas related to movement are broadly awake. The former explains why the sleeper is so out of control, confused, and lacks full vision; the latter why the person can move freely. The emotional centers of the brain and the lower part of the brain essential for a sense of balance are also activated. Interestingly, the memory region of the brain, a seahorse-like structure located behind the ears, is turned off. That is why the sleeper cannot remember these sleepwalking expeditions.
While it’s not known exactly what would cause the brain to enter this bizarre state of sleeping and waking simultaneously, genes play a role. In fact, a person can experience sleepwalking 10 times more frequent if a close relative (a first degree relative) also experiences it. You also have a more than 5% chance of experiencing it if your identical twin (who shares 100% of their genes) does compared to your non-identical twin (who shares 50%).
Stress can also trigger sleepwalking, or at least make it more frequent and severe in people with these genes. Mental anguish is a major source of brain arousal that is difficult to turn off at night, known as nocturnal arousal. A striking example is those who have experienced trauma. a recent study showed that PTSD patients have more and more awakenings than healthy people, they simply cannot maintain their sleep.
People who experience trauma are more likely to wake up during deep sleep because their overall sleep architecture is fragmented. Due to an awakened “emotional brain,” particularly an almond-like structure buried behind the ears called the amygdala, a person who has experienced trauma tends to fall asleep and wake up. The amygdala, which makes us feel restless and fearful, dances with activity in people with trauma and has surprisingly often exploded in size compared to people without trauma.
In addition, people with trauma also have fewer and thinner nerve fibers, running from the front of the cortex and your emotional brain that help keep it in check, similar to the brakes on a car. Your emotional brain practically has free rein, making your brain vulnerable to arousal during the deepest sleep.
Uncontrollable excitement and the inability to sleep soundly also explain why this phenomenon is common in children in particular. in about 80% of the cases. sleepwalking disappears when children become adolescents. This is because the frontal cortex is not fully mature in children. You just can’t control your nightly arousal, which ruins the depth of your sleep.
The human brain is far more mysterious than one might imagine, and sleepwalking (and the study of it) provides insightful insights into consciousness. It shows us that what we call consciousness is not a single one-dimensional thing. Instead, it can sometimes represent distinct states, each with unique flavors. Yet other times, as this phenomenon elegantly illustrates, they can merge, producing mixed brain states that blur the sharp line between what it means to be asleep and awake.
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