tickling me?!

You know when someone next to you is falling asleep, and they twitch? Or when YOU'RE going

to sleep and you feel that falling sensation… It's a thing, and it's normal. Humans twitch

involuntarily as they're moving from consciousness into unconsciousness -- called the hypnogogic

state. 60-70 percent of people have these twitches, but they usually don't remember

actually having them, because they're asleep! That makes them really difficult to study,

but that doesn't stop sleep scientists!

Science refers to sleep twitching as myoclonus (my-AH-klen-us), and the actual twitch itself

is called a hypnagogic jerk. There's no sleep switch in the brain. When you're awake, your

conscious brain is in control, and as you fall asleep, the unconscious processes are

taking over. Like a shift change at a factory, the handoff has lots of little things that

have to go right for the brain allow sleep to set in. Two parts of the middle of the

brain handle this transition, the reticular activating system (RAS), and the ventrolateral

preoptic nucleus (VLPO). They're in the middle of the brain, next to each other, right behind

the eyes. The RAS handles awakeness and the transition to sleep. The VLPO controls you

when you ARE asleep. The RAS and the VLPO are the factories handing off to each other,

in my earlier analogy.

During this transition, the brain stops sending out serotonin. You've probably heard of that

chemical, serotonin is what helps keep us happy, low levels of serotonin are an indicator

depression. But, serotonin ALSO helps us control our large muscles -- the ones in our arms,

and legs so we don't move too much -- but serotonin doesn't control tiny muscles in

our wrists, eyes and lips. 90 minutes into sleep, two neurotransmitters GABA and glycine,

work together to paralyze you so you don't get up and run around in real life… but

during that waking-sleeping handoff you're not there yet.

So, one hypothesis says the twitches come because you're starting to dream, but aren't

fully paralyzed. Your RAS is struggling with the VLPO, the serotonin levels are dropping,

body processes are being handed over, and the hypnagogic jerk is a symptom of misfiring

nerves as these two fight it out. An evolutionary hypothesis says this was a way to wake our

primate ancestors before they fell out of a tree -- because the jerk, also known as

a sleep start, causes muscles to react quickly.

In the end, we're not EXACTLY sure what's happening. But we DO know, that severe twitches

CAN be a sign of Parkinson's or Alzheimer's, the result of a brain injury, nerve damage

or fibromyalgia, but that's usually if it's a lot of SERIOUS twitching.

A new study in Current Biology says the twitches help baby's brains learn how to move their

limbs more accurately. They found the brain activity of anaesthetised rats was more vigorous

during sleep movement than during actual, awake movement! The researchers determined

it was the brain practicing and learning how to make their limbs move properly. So maybe

these twitches are a holdover? Who knows. More research is needed for sure.

Did you ever twitch so hard you woke up?! Sometimes I remember my twitches, it's weird.