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If you don't get enough sleep at night, be sure to drink a strong cup of coffee before trying to remember important facts, otherwise your sleep-deprived mind will play tricks with your memory, according to a European study. A loss of sleep impairs the mind's ability to recall facts efficiently. Still in a dream-like state, the mind jumbles the memory so that you may claim with high confidence to remember things that in fact never happened, typically due to strong semantic associations with actually encoded events, say the researchers at four universities in Germany and Switzerland. In other words, sleep deprivation prevents the mind from finishing its sorting and storing of memories. It is a bit like your computer warning you that some unsaved files may be lost if you reboot your computer without waiting for it to save everything first. A good jolt of caffeine, however, is often enough to speed up the "saving files" process so that memories are all sorted and clear, say the researchers in the journal Popular Library of Science One (PLOS One). Sleep is known to provide optimal neurobiological conditions for consolidation of memories for long-term storage, whereas sleep deprivation acutely impairs the retrieval of stored memories. The researchers found that sleep deprivation at the time of memory retrieval resulted in false memories. Test subjects who had a good night's sleep were able to remember new facts perfectly, while those who had not had enough sleep remembered "false facts", the researchers found. They also found that caffeine prevented inaccurate memory retrieval.
"Sleep deprivation at retrieval, but not sleep following learning, critically enhanced false memories of theme words. This effect was abolished by caffeine administration prior to retrieval," writes Susanne Diekelmann from the University of Luebeck in Germany. Subjects were divided into three groups and were given new facts to learn. Two groups learned in the evening and were tested the next morning, after they had either slept or stayed awake during the intervening night. The third group learned in the morning and was tested in the same evening after normal daytime wakefulness. The test subjects learned lists of semantically associated words like "night", "dark", "coal" but without the strongest common denominator, in this case "black". Those who were sleep-deprived later insisted that the word "black", for example, had been on the list when in fact it had not been on the list. Those who had "slept on it" correctly stated that "black" was not on the list. "Subjects of the 'night wake' group, who were acutely sleep-deprived at the time of retrieval testing, exhibited significantly more false memories than subjects in the two other groups," Diekelmann writes. Those subjects falsely recognized 88 percent of the theme words, whereas after a good sleep and daytime wakefulness false memory rate was negligible. A good strong dose of caffeine cleared the cobwebs from the minds of the sleep-deprived test subjects so that they remembered correctly that "black" had not been on the list, contrary to their initial - false - memories. 2009-07-09
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