—People in their 70s and beyond seem to need so much less sleep than they did when they were younger. New research from Beth Israel Deaconess Medical Center may finally explain why: They have lost sleep-promoting brain cells.
Working on animals, Beth Israel scientists had previously pinpointed a type of brain cell active mainly during sleep. When these neurons fire, they release a chemical called galanin that quiets brain signaling, allowing for sleep.
These cells have been found in the brains of rats, mice, cats, and monkeys — all in roughly the same area. Lab animals deprived of these brain cells sleep about 50 percent less at night and are tired all day, said Clifford Saper, chairman of Beth Israel’s Department of Neurology, and leader of the new research.
Scientists had seen similar cells in people, but until now it was not clear that they really controlled human sleep they way they do in animals.
In the new study, published in the journal Brain, Saper shows that the numbers of galanin-producing nerve cells are reduced in older people, and particularly in Alzheimer’s disease.
“There’s a very tight correlation between the number of these cells you have in your brain and how you sleep,” Saper said.
The number of remaining cells also predicts the person’s wake-sleep behavior, and how deeply they slept.
“The people who had the most nerve cells left slept the best; the ones with the least had the most disrupted sleep,” he said.
One of the most common reasons for putting Alzheimer’s patients in nursing homes is their tendency to wake up at night and wander, sometimes outside. “We think it’s due to the loss of these neurons,” Saper said.
The study, which also included researchers from Rush University in Chicago and the University of Toronto, piggybacked on a Rush study of 1,000 older people, followed for 15 to 20 years, until their deaths. Study participants periodically wear a wristband to track daily activities — when they are inactive for an extended time, they can be presumed to be sleeping.
In 45 study participants, Saper’s team was able to match cell counts of the galanin-producing cells after death with the person’s sleep patterns when they were alive.
The study is very well done, despite the challenge of explaining activity deep inside the brain, said Ronald Szymusiak, a sleep researcher at the David Geffen School of Medicine at the University of California Los Angeles, who was not involved in the study.
He said the study confirms for him that rodents, despite obvious differences, have similar brain activity to people when it comes to sleep.
“It suggests it might be worthwhile to take another look at these neurons in animals,” Szymusiak said. “It might be a mechanism by which the formal process of aging results in more fragile, fragmented sleep.”
Because the cells release the neurotransmitter galanin, it is possible Szymusiak said, that adding galanin to the brains of older people and Alzheimer’s patients will help correct sleep problems — but he said he is not aware of any research to do this.
Sleep is increasingly being seen as a “third pillar of health,” along with exercise and nutrition, he said. Many health problems bring related sleep difficulties, so it hasn’t been clear whether reduced sleep is a natural part of aging, or whether other health conditions, which mount with age, reduce sleep.
Lack of sleep clearly contributes to other health problems such as diabetes, blood pressure, and heart disease, said Saper.
It’s not yet clear whether boosting galanin-producing cells would help reduce these health problems or boost healthy aging. But it may be worthwhile to develop ways to maintain these intermediate nucleus cells or grow more. “That would certainly be a terrific goal for future research,” Saper said.