Infants spend twice as much time in REM sleep as adults—but experts still know little about what happens in their brains during those hours.
Infants spend most of their time sleeping, waking up for just a few hours total every day. A lot of growth happens during those spans of shut-eye, though. Research shows that sleep is just as formative for babies’ development as are the scattered bouts of consciousness when their eyes are open and their ears are perked up. As with adults, sleeping likely helps infants retain or protect memory and learn language; some evidence also suggests it promotes healthy physical growth. Technological advances are helping to shed more and more insight on, as the University of Washington professor of early-childhood learning Patricia Kuhl has put it, “the infinite number of secrets” contained in babies’ brains.