Ebbinghaus showed that if you learned syilables that do not exist in your language, over time you forget with very characteristic exponential decay and this also true in humans, in rats, in bees, this is a general law of learning, you forget what they did was to replicate this classical experiment, but they had the subjects either stay awake, going to some college class, or sleep in between the acquisition and testing, and what you see is that sleep protected those memories it's much better to sleep than going to classes, if you want to remember stuff that is not in the classes so this finding was not followed up until the 60's, for reasons I don't quite understand but then in the 60's there was a surge of interest in this kind of study using animal models mice and rats in particular, and this happened in the US and happened in France, who were actually competing for who was to own REM sleep/paradoxical sleep and then in the 70's a lot of people published papers like this, saying that sleep deprivation impairs learning, and then there was this discussion about the confounds of sleep deprivation whether this is stress or not, there was some protocols in the 90's, Bob Stickgold in Harvard was able to show that you can discount stress from your preparations making some arrangements so that you can convince people that it's really sleep that is doing the trick 