207 healthy Harvard students were recruited by Jessica Payne from the University of Notre Dame, Indiana for this study. The participants were assigned to study semantically related or unrelated word pairs at 9am or 9pm.
The researchers then tested the participant's ability to recall the word pairs 30 minutes, 12 hours, or 24 hours later depending on experimental condition.
|Test design: white indicates wakefulness; dark gray indicates sleep. Image: Memory for Semantically Related and Unrelated Declarative Information: The Benefit of Sleep, the Cost of Wake, Jessica D. Payne et al, Plos One.|
But subjects who slept between tests were significantly better at remembering the unrelated words than those who got no shuteye.
In the 24-hour retest—where all subjects had a full night of sleep—those participants who went to bed shortly after learning the words did much better than those who went through an entire day before sleeping.
So if you need to remember something, try reviewing those notes just before bedtime. But if you want to forget something, a heartbreaking breakup for example, do not sleep over it -- you might end up enhancing the painful memory.
info: Memory for Semantically Related and Unrelated Declarative Information: The Benefit of Sleep, the Cost of Wake, Jessica D. Payne et al, Plos One. doi:10.1371/journal.pone.0033079.g001