Why Might Sleep Help Preserve New Word Pairs?

After studying new words and then sleeping, you may feel you remember more than you would after staying awake all day. The common misunderstanding is that sleep somehow inserts things we never learned into memory. A better question is what happens to material already learned during a period of sleep compared with a similar stretch of wakefulness.

In a peer-reviewed experiment, participants learned word pairs that were either semantically related or unrelated, in the morning or evening, and were tested after different intervals. Training time did not alter initial performance. At twelve hours, the group whose interval included a night’s sleep performed better overall than the group whose interval involved daytime wakefulness. Looking at the materials separately, the difference mainly reflected greater forgetting of unrelated pairs during wake; related pairs did not show the same sleep–wake advantage. That is more precise than saying sleep strengthens every memory: existing links and newly formed links behaved differently.

Sleep and wake also involve different activities and possible interference, so this comparison alone cannot assign every part of the difference to one neural mechanism. The experiment tested particular word pairs over particular intervals, not whole courses, everyone’s sleep habits or a guarantee for last-minute cramming. My practical judgement is to learn properly first and allow the memory a normal opportunity for sleep. Sleep is no substitute for understanding, nor is one study a timetable that suits everyone.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3310860/