(11) A human infant is born with a brain that is only 25% developed. Babies’ brains grow rapidly in the first two years of life -- up to 70% of their adult size. Hundreds of trillions of neural connections are established and billions of nerve cells develop. It’s a majestic biological orchestration requiring a great deal of REM sleep. Babies spend most of their nighttime hours in REM sleep (much more than adults) and this contributes to their frequent night waking and notorious patterns of light sleep. While frustrating for parents, these patterns are actually healthy for babies. During REM sleep, key proteins central to the construction of nerve cells are manufactured and blood flow in the brain doubles. Consider that premature babies spend 90% of their sleep time in REM.