Why is it when I fall asleep I get all twitchy?
Am I dying?! Am I trying to escape? Are ghosts 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.