Do We


Sleep enforces memory temporal sequence

April 16,2007

LUBECK, Germany, April 18 (UPI) -- German scientists have determined how the brain keeps track of the temporal sequence of memories.

People usually have good memories of some past events, but it's not been clear how the brain keeps track of the temporal sequence of memories -- did Paul spill his glass of wine before or after Mary left the party?

Jan Born and colleagues at the University of Lubeck have confirmed the theory that long-term memories are formed during sleep, while the brain replays recently encoded experiences.

Born and colleagues determined sleep not only strengthens the content of a memory, but also the order in which a memory was experienced, probably by a replay of the experiences in "forward" direction.

Students were asked to learn triplets of words presented one after the other. Then some slept while a control group remained awake. The students were then presented the words and asked which came before and which came after during the learning session.

The researchers discovered sleep enhanced the rested students' word recall, but only when they were asked to reproduce the learned words in a forward direction.

Study: Lack of sleep can affect learning:

BOSTON, Feb. 15 (UPI) -- U.S. scientists have determined sleep deprivation impairs memory for subsequent experiences by altering the function of the hippocampus.

Sleep researchers have known sleep occurring after an experience can be critical to learning and memory but in the new study Matthew Walker and colleagues at Harvard University Medical School found sleep before an experience is also critical for the normal functioning of memory systems.

The scientists deprived people of a night's sleep and then asked them to observe and remember a large set of picture slides for a subsequent recognition test. Following a full night's sleep, the subjects were queried about the slides.

The researchers found sleep-deprived subjects showed decreased activity in the hippocampus -- a brain region important for memory -- relative to control subjects who were not sleep-deprived while viewing the pictures; sleep-deprived people also had poorer subsequent recall abilities.

The relationship of activation in other brain areas to activation in the hippocampus was also altered, suggesting sleep deprivation alters memory-encoding strategies, the researchers reported.

The study appears in the March issue of the journal Nature Neuroscience.

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