Catching Zs may snag memories, too

Sleep can restore the memory of profoundly forgetful fruit flies. That raises the possibility that promoting sleep in people with Alzheimer’s disease and other memory disorders might ease their symptoms, too.

The flies were able to overcome memory-stealing mutations with something as simple as some solid rest, scientists report online April 23 in Current Biology. “Quite honestly, this is a stunning result,” says study coauthor Paul Shaw of Washington University in St. Louis. “We take flies that are bad and we make them better. We don’t just prevent their deficits. We reverse them.”

If the fly research, on Drosophila melanogaster, can be translated to people, the results suggest that “we ought to take the frequent sleep disturbances in the aging population much more seriously,” says neuroscientist Maiken Nedergaard of the University of Rochester Medical Center in New York. It’s possible that even simple sleep-promoting habits such as exercise and less caffeine might benefit people with memory trouble, she says.

Although it’s a leap from insects to people, fruit fly sleep actually looks a lot like people’s: Sleeping flies hold very still and are hard to rouse. Shaw and his colleagues increased sleep time in flies that had several different mutations known to cause severe memory problems.

When coaxed to sleep more with the drug THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol), these formerly befuddled flies got sharper, the team found. In a test of short-term memory, flies better remembered to avoid an area laden with the nasty chemical quinine. These well-rested flies could also hold a memory over several days. Male flies learned not to waste time courting male flies that smell like females: Two days after the failed courtship, these male flies remembered their rejection and didn’t attempt to woo their unwilling recipients.  

The team got the flies to conk out two other ways, too — by activating certain brain cells and by increasing the levels of a protein. Both methods also led to memory boosts, suggesting that the benefits are due to sleep and not an effect of a drug. “It’s not how you make them sleep,” Shaw says. “It’s that they sleep.”

Researchers also investigated flies with mutations in the fly version of Presenilin, a gene linked to inherited, early-onset forms of Alzheimer’s disease. Sleep could improve long-term memory in these flies as well.

The results tie into a growing body of work that’s revealing a complex relationship between sleep and Alzheimer’s disease, says neurologist Mark Wu of Johns Hopkins University. Clinicians have known for a long time that people with Alzheimer’s often sleep poorly, but the work of Wu and others suggests that poor sleep could also exacerbate the disease. “We didn’t really appreciate until recently [that] possibility,” he says.

Right now, the research is preliminary, Wu cautions. “It’s a stretch to suggest that sleeping would cure memory problems in Alzheimer’s disease patients,” he says. “But there’s a potentially important relationship between sleep and Alzheimer’s disease,” and the implications of that relationship are large. “Functionally, we cannot treat Alzheimer’s at all,” he says. “Sleep stuff, we can treat.”