Sam Kean - The Tale of the Dueling Neurosurgeons: The History of the Human Brain as Revealed by True Stories of Trauma, Madness, and Recovery

I cant fall asleep on my backor rather, I dont dare to. In that position I often slip into a fugue state where my mind wakes up from a dream, but my body remains immobile. In this limbo I can still sense things around me: sunlight trickling through the curtains, passersby on the street below, the blanket tented on my upturned feet. But when I tell my body to yawn and stretch and get on with the day, nothing happens. Ill recite the command againMove, youand the message echoes back, unheeded. I fight, I struggle, I strain to twiddle a toe or flex a nostril, and it does no good. Its what being reincarnated as a statue would feel like. Its the opposite of sleepwalkingits sleep paralysis.

The worst part is the panic. Being awake, my mind expects my lungs to take full, hearty breathsto feel my throat expanding and my sternum rising a good six inches. But my bodystill asleep, physiologicallytakes mere sips of air. I feel Im suffocating, bit by bit, and panic begins to smolder in my chest. Even now, just writing this, I can feel my throat constrict.

As bad as that sounds, some sleep paralytics have it worse. My episodes dont last that long: by concentrating all my energy, Zen-master-like, on twitching my right pinky, I can usually break the trance within a few minutes. Some peoples episodes drag on for hours, full nights of torture: one Korean War vet reported feeling more terror during a single episode of sleep paralysis than during his entire thirteen months of combat. Other people nod off narcoleptically and slip into this state during the day. One poor woman in England has been declared dead three times and once woke up in a morgue. Still other people have out-of-body experiences and feel their spirits careening around the room. The unluckiest ones perceive an evil presencea witch, demon, or incubuspressing down on their necks, smothering them. (The very mare in nightmare refers to a witch who delights in squatting on peoples chests.) Nowadays people sometimes weave this feeling of paralysis into alien abduction stories; presumably theyre strapped down for probing.

Sleep paralysis doesnt actually open a portal into the supernatural, of course. And despite what I may have thought when young, sleep paralysis doesnt offer proof of dualism, either: the mind cannot appear outside the body, independent of it. To the contrary, sleep paralysis is a natural by-product of how our brains work. In particular, its the by-product of faulty communication among the three major parts of the human brain.

The base of the brain, including the brainstem, controls breathing, heart rate, sleeping patterns, and other basic bodily functions; the brainstem also works closely with the nearby cerebellum, a wrinkly bulb on the brains derriere that helps coordinate movement. Together, the brainstem and cerebellum are sometimes called the reptile brain, since they function approximately like the brain of your average iguana.

The second part, the so-called mammal brain, sits deep inside the skull, just north of the brainstem. The mammal brain relays sensory input around; it also contains the limbic system, which helps capture memories, regulate emotion, and distinguish between pleasant and rotten experiences. Unlike the instinct-driven reptile brain, the mammal brain can learn new things quite easily. To be sure, some neuroscientists deride the mammal/reptile division as too simplistic, but its still a useful way to think about the brains lower regions.

Both of these nether regions control automatic processes, things we dont think about, or want to. This autopilot frees up the outermost part of the brain, the primate brain, for advanced duties, especially in humans. We can further divide the wrinkly primate brain into four lobes: the frontal lobes (near the front of the brain), which initiate movement and help us plan, make decisions, and set goals; the occipital lobes (back of the brain), which process vision; the parietal lobes (atop the brain, the pate), which combine vision, hearing, touch, and other sensations into a multimedia worldview; and the temporal lobes (side of the brain, behind the temples), which help produce language, recognize objects, and link sensations with emotions.