Study of sleeping fur seals provides insight into the function of REM sleep

All land mammals and birds have two types of sleep: rapid eye movement (REM) and non-REM (also called slow-wave sleep). Earlier evidence had suggested that REM sleep is essential for physical and mental well-being and learning, but the underlying function of REM sleep has been a mystery. New insight into the function of REM sleep, based on studies of an unlikely animal: the fur seal.