Some animals - such as dolphins and whales - are able to "sleep with half their brain". One side of the brain goes into sleep-mode activity while the other remains awake.
But a remarkable new study has revealed that something similar may happen in humans as well - every night.
The research used a combination of scalp EEG, and electrodes planted inside the brain, to record brain activity from 5 people undergoing surgery to help cure severe epilepsy. The subjects were then allowed to go to sleep for the night, while recording took place.
As expected, after falling asleep, the EEG showed delta wave activity - strong, slow waves of electrical activity (0.5 to 4 Hz) which are typical of deep, dreamless "slow wave sleep".
However, the electrodes inside the brain told a different story. While they recorded delta waves most of the time, they also showed that there were ...
