Going night after night without sleep makes us absent minded, and now we may know why
Going night after night without sleep makes us absent-minded, and now we may know why. In rats, sleep deprivation causes stress hormones to accumulate in a part of the brain called the hippocampus, which in turn stunts the growth of cells that lay down new memories.
“This decrease in neuron production coincided with an increase in the major rodent stress hormone, corticosterone,” says Elizabeth Gould, head of the team at Princeton University that made the discovery. When Gould stopped production of the hormone in rats by removing their adrenal glands, the animals carried on producing new neurons as normal despite being deprived of sleep (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0608644103).
“We concluded that sleep deprivation decreases neurogenesis by elevating stress hormones,” says Gould. The results tally with earlier studies showing that sleep-deprived people are worse at remembering how to do newly learned tasks than they are normally. “We know that sleep deprivation is stressful, and that it impairs certain types of learning and memory,” she says.
Derk-Jan Dijk of the Surrey Sleep Research Centre at the University of Surrey in Guildford, UK, says the results are the first to provide a plausible mechanism explaining how a lack of sleep damages memory. “It points to the importance of sleep in the right hormonal conditions,” says Dijk. “These are altered if you sleep at the wrong time of day, or if you are stressed generally,” he says. The results explain how shift work might damage memory by producing “a different hormonal milieu”.
“The results are the first to provide a plausible mechanism explaining how a lack of sleep damages memory”
However, Tarja Porkka-Heiskanen of the University of Helsinki in Finland says that may be going too far, as the 72 hours of sleep deprivation experienced by the rats is exceptionally long, equivalent to several days in humans. Sleep deprivation can damage memory, but only “in extreme cases”, she believes.