Half-asleep rats look wide awake

Some parts of a rat’s brain can fall asleep even while the animal plays and seems wide awake, a new study shows.

Researchers at the University of Wisconsin–Madison and their colleagues in Italy kept rats up four hours past the rodents’ usual bedtime. Even though the rats stayed awake, electrodes implanted in their brains showed that some brain cells went to sleep while neighboring ones remained active, the team reports in the April 28 Nature.