Are You Asleep or Are You Awake? Or Are You Both at the Same Time?!!!!
Have you heard of asymmetrical sleep? It means that one side of the brain is less active, sometimes experiencing deep sleep while the other side remains active, or awake. Usually, both hemispheres of the brain have similar or symmetrical brain activity when you sleep. Many mammals and birds have periods of time when one half of their brain is awake while the other hemisphere is sleeping, allowing them to remain alert while still getting some shut-eye. This aids in avoiding predators or other potential dangers. Also, birds in migration and other animals on the move can still sleep while their body keeps going. But, this is not sustainable in the long term as this activity only allows for 8% of the typical sleep an animal gets when in full sleep mode. Too much of this brings on the effects of sleep deprivation.
The question is, do humans experience asymmetrical sleep too? A 2016 study indicates we do. While most of the time our brain hemispheres are more simultaneous in their active and resting states, believe it or not, there are times when our brains don't symmetrically fall asleep. What causes this state in the human brain? The main culprit appears to be what is deemed the "first night affect" you might experience in a new sleep space such as a hotel room. While you are unlikely in danger, your body reacts via an asymmetrical sleep state just to be sure.
Check out this fascinating 5-minute TED Ed Talk by Masako Tamaki to learn more.