You go to sleep at night, you wake up in the morning---the definition of sleep doesn't seem so complicated. But start asking questions and things start getting thorny: Are dolphins that never stop swimming
sleeping? Are migrating birds that "shut down" half their brains
sleeping? Is someone under general anesthesia sleeping? And what about babies in the womb? Unborn human babies in the womb are pretty difficult to monitor 24/7, so the researchers interested in that last question got ahold of unhatched chicken eggs. In a new Current Biology paper
, they report that chicks show higher-brain activity patterns similar to sleep, and the cries of a hen could "wake up" the chick even when other loud but not chicken-salient sounds could not. These higher-brain activity patterns only appear in the last stage of incubation, presumably after their brains become well developed. To monitor brain activity in the chicks, the ...
