Memory Linked to Sleep

People who sleep after processing and storing a memory carry out their intentions much better than people who try to execute their plan before getting to sleep. Researchers at Washington University in St. Louis say they’ve shown that sleep enhances our ability to remember to do something in the future, a skill known as prospective memory.

That’s one of the key findings of a study published recently in Psychological Science by researchers Michael Scullin and  Mark McDaniel, PhD.  They’re focusing on “prospective memory” — things we intend to do — as opposed to “retrospective memory” — things that have happened in the past.

Prospective memory includes such things as remembering to take a medication, buying a Mother’s Day card or bringing home the ice cream for a birthday party. While the vast majority of sleep literature in psychology is devoted to retrospective memory, this study is the first foray into the relationship between sleep and prospective memory, the kind of memory we put to work every day. The findings, researchers say, offer important contributions to the understanding of the role sleep plays in cognition as well as memory.

he researchers tested four different groups each of 24 Washington University students. Two were control groups — one tested in the morning, the other in the evening — to eliminate the notion that the biological clock might play any role in memory function. Another group was prepped for tests in the morning then tested twelve hours later in the evening before getting to sleep. The fourth group learned the test routine in the evening, went home and slept, then were tested 12 hours later in the morning.

Participants were given instructions for three tests in this order and the tests later were given in blocks of 150 items in the same order: a living/non-living test, in which they decided if a word (cat, for instance, or skate) indicated a living or non-living entity; a lexical decision test, in which participants decided if a string of letters was a word or nonsense; and a semantic category test, in which a word was classified by participants into a category, baseball, for instance, in the category of sport.

After learning the last test, participants were told that in the midst of these ongoing tests — given to represent such everyday activities as driving, watching TV, listening to a teacher — the words table or horse would pop up on a screen, and when they saw them, they were to press the “Q” button. This represented the prospective memory intention.

The researchers found that participants who tested in the morning following sleep overwhelmingly performed the prospective memory task better in the semantic category test, or context, than in the other two, and they found no such correlation in the group who tested sleepless.

“Sleep promoted the remembering to do the prospective memory task when that one context was present, but not when some other context was present,” McDaniel says.

Visit the Washington University website to read more on the study.