Order of non-REM and REM sleep
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Both Gina and Bob suggested non-REM sleep first plays a memory function and then REM sleep is either 'creative' with the memories (Bob) or 'cleans up' further (Gina). In neonates the order is reversed - REM sleep occurs at sleep onset, and then non-REM - but babies still have multiple cycles before awakening. So the concept seems to hold that they have multiple cycles in case, if they are wakened early, they'll have had at least one cycle which includes BOTH states, indicating the two have to occur together to be efficacious.