By tracing sleep-related neural signals to a specific region of the lizard’s brain—and linking that region to a mysterious part of the mammalian brain—a new study suggests complex sleep evolved even earlier in vertebrate evolution than researchers thought, reports Science.
“Answers to the questions raised and reframed by this research seem extremely likely to be significant in many ways, including clinically,” says Stephen Smith, a neuroscientist at the Allen Institute who was not involved with the new study.
Mammals and birds have two kinds of sleep. During rapid eye movement (REM) sleep, eyes flutter, electrical activity moves through the brain, and, in humans, dreaming occurs. In between REM episodes is “slow wave” sleep, when brain activity ebbs and electrical activity synchronizes.