Checking Brain Chemical Key for Memory

Low levels of acetylcholine crucial during sleep, study finds

WEDNESDAY, Jan. 28, 2004 (HealthDayNews) -- Low levels of a key chemical messenger in the brain are crucial during sleep if you are going to form long-term memories.

That's the conclusion of German researchers, who publish their findings in this week's issue of the Proceedings of the National Academy of Sciences. They suggest their discovery might warrant a closer look at how certain medications are given to Alzheimer's patients.

For decades, scientists have known that levels of the chemical messenger, acetylcholine, must be adequately high during wakefulness for learning new things. "Our study now is the first one to show that for memory consolidation -- that is, strengthening newly acquired memories -- low levels of acetylcholine in the brain during sleep are a prerequisite," says lead researcher Steffen Gais, with the department of neuroendocrinology at the University of Lubeck, Germany.

While Gais concludes the current practice of giving Alzheimer's disease patients medicine to keep their acetylcholine levels high during sleep should be re-evaluated, an Alzheimer's disease expert says much more study is needed before medication changes are warranted.

The drugs commonly given Alzheimer's patients are called cholinesterase inhibitors and are designed to enhance memory and other cognitive functions. Cells that use acetylcholine are damaged or destroyed in the brains of Alzheimer's patients, so they have lower overall levels of the chemical messenger. The cholinesterase inhibitors slow the natural breakdown of acetylcholine, thus keeping levels high.

For the study, Gais tested the performance of 29 healthy men, aged 18 to 35, giving them different memory tasks. They learned a word-pair list and performed a mirror tracing task. After studying the list of word pairs, they were told one word and asked to name the second one in the pair. In mirror tracing, subjects were asked to trace several figures that they could only see in a mirror, as quickly as possible.

They did the tests before sleeping. Half were given a drug to keep their acetylcholine levels high during sleep; half were not.

The researchers awakened the men during the night and had them repeat the tests. No differences were found in performance on the mirror-tracing, but those who were given the drug to keep acetylcholine levels high performed worse on the word-pair test than those not given the drug.

Gais says the study supports the idea that low acetylcholine levels are needed during sleep to strengthen newly acquired memories.

The study can't yet make definitive conclusions about the use of drugs to affect acetylcholine levels in Alzheimer's patients, Gais says. "However, further studies have to investigate whether drug administration should be moved away from the evening hours."

But William Thies, vice president of medical and scientific affairs at the Alzheimer's Association, says that while calling for more research is perfectly valid, the study results are by no means a reason for any Alzheimer's patient to change medication on his or her own.

"This study was not done on patients with Alzheimer's or people with memory problems, but on young, healthy people," Thies says. "It is very difficult to draw broad conclusions about giving medication to Alzheimer's patients based on this study."

But research to investigate optimal timing of medication for Alzheimer's would be welcomed, he says.

More information

For more information on cholinesterase inhibitors, go to the Alzheimer's Association. Learn more about sleep at the American Academy of Sleep Medicine.

SOURCES: William Thies, Ph.D., vice president, medical and scientific affairs, Alzheimer's Association, Chicago; Steffen Gais, scientific assistant, Department of Neuroendocrinology, University of Lubeck, Lubeck, Germany; Jan. 26-30, 2004, Proceedings of the National Academy of Sciences
Consumer News