To Sleep … Perchance to Learn

Researchers may have found the reason why children who go to bed too late often fare badly at school: lack of sleep appears to disrupt functioning of the hippocampus, an area of the brain that formulates new memories.

Reporting in the journal Nature Neuroscience, Harvard Medical School investigators recruited 28 volunteers, who were either randomly deprived of sleep for two days and a night before carrying out a test or who were allowed to sleep normally.

The test involved looking at and remembering a large set of picture slides while the volunteers were screened by fMRI scanner, which gives a 3-D image of blood flow, hence of cerebral activity.

The human guinea pigs were then allowed two full nights of sleep and then performed a second test in which they were asked to spot the original slides in a batch that included new pictures.

The sleep-deprived group did slightly worse in the first test than the sleepers, but did considerably better than them in the second.

The scanner showed that, in the first test, hippocampus activity among the sleep-deprived was far lower than among their counterparts. This had a knock-on effect on other parts of the brain that are linked to alertness, the brainstem and thalamus.

Previous research has found that sleep after learning is vital for consolidating memory, but hard evidence has until now been lacking as to the effects of lack of sleep before a memory is created.

“These results demonstrate that an absence of prior sleep substantially compromises the neural and behavioral capacity for committing new experiences to memory,” says the paper.

“It therefore appears that sleep before learning is critical in preparing the human brain for next-day memory formation – a worrying finding considering society’s increasing erosion of sleep time.”

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