Mind Hacks has an intriguing piece on "Hypnic Jerks" -- the erratic movement of our legs and arms when we are asleep. The piece suggests that these are more than simply random muscle movements, but rather the result of a "battle in our brains". From the piece:
Normally we are paralysed while we sleep. Even during the most vivid dreams our muscles stay relaxed and still, showing little sign of our internal excitement. Events in the outside world usually get ignored: not that I’d recommend doing this but experiments have shown that even if you sleep with your eyes taped open and someone flashes a light at you it is unlikely that it will affect your dreams.
But the door between the dreamer and the outside world is not completely closed. Two kinds of movements escape the dreaming brain, and they each have a different story to tell.
Read the entire piece at Mind Hacks.
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