03 November 2008

Tired brains create false memories

If you don't get enough sleep at night, be sure to drink a cup of coffee before trying to remember important facts – otherwise your mind will play tricks with your memory.

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 team of German researchers.

Lack of sleep impairs the mind's ability to recall facts efficiently. Still in a dream-like state, the mind jumbles 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 Luebeck University, Heinrich Heine University in Dusseldorf and the universities of Geneva and Zurich.

In other words, sleep deprivation means the mind has not finished sorting and storing memories. It is a bit like when your computer warns you that some unsaved files may be lost, if you reboot your computer without waiting for it to save everything first.

But a good jolt of caffeine is often sufficient to speed up the "saving files" process so that memories are all sorted and clear, the researchers write in the journal Popular Library of Science One (PLOS One).

Sleep good for memory
Sleep is known to provide optimal neurobiological conditions for consolidation of memories for long-term storage, whereas sleep deprivation acutely impairs retrieval of stored memories.

The German 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. Those who had not had enough sleep remembered "false facts," the researchers found.

They also found that caffeine prevents the inaccurate memory retrievals.

"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 Dr Susanne Diekelmann of the Department of Neuro-Endocrinology, 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 had learned lists of semantically associated words, such as "night", "dark", "coal" but without the strongest common denominator or theme word - such as "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.

Frequent false memories
"Subjects of the 'night wake' group, who were acutely sleep deprived at retrieval testing, exhibited significantly more false memories than subjects in the two other groups," Diekelmann writes.

Those subjects falsely recognised 88% of the theme words, whereas after sleep and diurnal wakefulness false memory rate was negligible, she writes.

"Importantly, subjects did not produce more false memories in the 'night sleep' group than in the 'day wake' group, which would be expected, if consolidation processes during post-learning sleep were critical for the development of false memories," the author points out.

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 memories - false memories. – (Sapa-dpa)

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