A couple of decades ago, many people thought you could learn while you sleep. I remember as a college student playing audio tapes of information I wanted to learn while I slept. This idea turned out to be a fraud, perpetrated by people who sold sleep learning materials and equipment. Most "early adopters" found that all it did was disrupt sleep.
But as I have discussed elsewhere, modern research has compellingly shown that the brain is consolidating memories of the day's events during sleep. So, maybe the sleep learning idea is not completely dead. Maybe the right kind of stimulus input while you sleep could promote learning, at least in terms of promoting memory consolidation of the information you already learned during the day.
So, the idea would be to see if sleep can promote memory consolidation of things you recently learned, but have not yet formed into lasting memory. How might you do that? Since memory is largely associative, maybe it would work to provide during sleep the cues that were associated with the original learning. This might have a better chance of working during the dream stage of sleep, because it is well documented that external sound stimuli (like storms, rain, etc.) are documented as capable of becoming incorporated into and changing the course of a dream. Thus, the question becomes: can audio presentation of learned association cues during dreaming promote the memory formation for the original learning items or events. The idea is that the cue might reactivate a latent memory and thus constitute a memory rehearsal.
Partial testing of this idea has recently been reported. Northwestern University scientists trained human subjects to recognize the location of 50 different objects on a computer screen. Each object had an associated sound. For example, the cat image was associated with a meow sound, a kettle with a whistle, etc. Then people took a nap, during which sound cues were presented (unobstrusively at 62 decibels) for half of the images they had previously been exposed to. After the nap, subjects had no conscious recollection of the sound cueing.
The cues were presented oddly enough only during the deep stages of sleep, not during dreaming. Maybe the researchers were unaware that external stimuli can get incorporated into dreams. Even so, the original objects were re-presented after waking and subjects tested for recall of the location of the 50 images.
Measuring the location errors in terms of distance from correct position indicated that accuracy was greater for images that had associative cues presented during the nap than for those images for which cues were not re-presented. Simultaneous recording of brain waves (EEG) showed that the brain was responding to the sensory cues during sleep.
Tests in control subjects, who were tested without the intervening nap, showed that the cues provided no improvement in recall.
The principle seems sound. What remains is for clever entrepreneurs to develop memory-enhancing strategies that are specific for specific learning tasks.
The old ideas of sleep learning are dead, but here is a new opportunity for finding ways to get sleep to work for us. Learning protocols have to be developed for specific learning tasks, and these have to have relevant sound cues. Finally, I suspect that such external learning "reminders" will be more effective when presented during dream sleep, not the deep stage of sleep in which people "fall into a pit" of oblivion. The challenge is to find ways to provide appropriate reminders while we sleep (or dream).
Source: Rudoy, J. D. et al. 2009. Strengthening individual memories by reactivating them during sleep. Science. 326: 1079.
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