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REM Sleep WindowsSome of the most impressive researchon REM sleep and memory to date isthat of REM sleep windows.Thenutshell of what this research shows isthat there are specific time windowsfollowinglearning duringwhich REMsleep must beallowed to occurin order for theconsolidation ofmemory tooccur. For NASA,there arespecificwindows in timeduring which itwould befeasible tolaunch a rocketor space shuttle.This is known asthe launchwindow. Simplystated, the REMsleep window isthe specific window of time for REMsleep to occur after learning, so thatthe material learned will then becomeconsolidated into the pre-existingmatrix of memories.

The concept of the REM sleep windowwas first developed while doingcontinuous long term brainwaverecording and REM sleep deprivationexperiments on rats while having themlearn trials in a rat training exercise.The studies involved teaching rats atask commonly used in rat memoryresearch called the shuttle avoidancetask. Each group of rats received 100training sessions.The first group of ratsreceived all 100 training sessions on

the first day.1 The second group of ratswere required to learn the task during2 consecutive daily sessions of 50 trialsper day,2 and the third group of rats tolearned the task in 20 trials per day

over 5consecutivedays.3 Thus,while all animalswere ultimatelyexposed to 100training trials inthis task, it wasthe distributionof sessions thatvaried.

For the rats thathad all 100training sessionson the same day,the increase inREM sleep wasthe greatest andwas also seen tohappen theearliest after the

end of training. For the other twogroups, REM sleep actually maximizedin two smaller peaks that were moredelayed from the training sessions.Therats that had 20 training trials over fivedays had the smallest increases in REMsleep. Rats that were trained but werenot able to learn and rats that werenever taught the task did not have thisincrease in REM sleep.The increase inREM sleep occurred during a narrowrange of time following training.Theseare the REM sleep windows.Preventing REM sleep from occurringduring these specific times wassufficient for preventing learning.4 Alsoquite interesting is that REM sleepdeprivation at any times other than the

specific REM sleep windows did notresult in any appreciable reduction inlearning.5

Since this initial research using theshuttle avoidance task in rats, thefinding of the importance of REMsleep windows has subsequently beenreplicated in a number of otherstandard rat research tasks, such as thecomplex operant appetitive task,6 theMorris water maze,7, 8 the 8-arm radialmaze,9 and a conditioned cuepreference task.10 The timing of theREM sleep windows may vary slightlyfor different types of tasks.This may bebecause different types of tasks entaildifferent kinds of learning. REM sleepwindows can also be seen inmonkeys.11

It is unclear as to whether the exacttiming of REM sleep windows differsfor different types of learning.Theresearch done to date implies thatonce something is experienced orlearned, there may be a finite amountof time that the event must beincorporated into memory. If we aredeprived of REM sleep during certaintimes of the night for a certain numberof nights following an event, our abilityto store that event or information maybe lost forever.12

1. Sleep, 1980, 3, 67-812. Physiology and Behavior, 1986, 36, 1053-1057.3. Sleep, 1980, 3, 67-814. Neuroscience and Biobehavioral Reviews, 1985, 9, 157-168.5. Canadian Journal of Psychology, 1991, 45, 115-124.6. Behavioral Neuroscience, 1991, 105, 282-288.7. Physiology and Behavior, 1996, 59, 93-97.8. Behavioral Neuroscience, 1997, l 11, l197-1204.9. Neurobiology of Learning and Memory, 1998a, 69, 211-217.10. Sleep, 1999, 22, S243.11. Journal of Neuroscience, 1989, 9: 1922-1936.12. Walter, T (2007) Chapter 12, REM Sleep Windows. In REM IlluminationMemory Consolidation (pp. 133-142), Grove City; OH: Lotus Magnus.

Grove City • East Columbus • Westerville • Canal Winchester

Timothy J. Walter, M.D.

Uma Marar, M.D.

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