Science

Loss of neurons, not lack of sleep, makes Alzheimer's patients drowsy – study

The findings contradict the common belief that Alzheimer's disease patients sleep during the day to make up for a bad night of sleep.

The tiredness that Alzheimer’s patients experience is not caused by a lack of sleep, but the system in their brain that keeps them awake no longer works, a new study suggests.

The findings contradict the common belief that Alzheimer’s disease patients sleep during the day to make up for a bad night of sleep, researchers say.

They could also point towards potential treatments to help these patients feel more awake.

The data came from people who were patients at UC San Francisco’s Memory and Ageing Centre in America and volunteered to have their sleep monitored and donate their brains after they died.

Being able to compare sleep data with brain tissue after death was the key to answering a question that scientists have been pondering for years.

Senior author, Dr Lea Grinberg, said: “We were able to prove what our previous research had been pointing to – that in Alzheimer’s patients who need to nap all the time, the disease has damaged the neurons that keep them awake.

“It’s not that these patients are tired during the day because they didn’t sleep at night.

“It’s that the system in their brain that would keep them awake is gone.”

Researchers say the opposite effect was seen in patients with other neurodegenerative conditions.

Those patients have damage to the neurons that make them feel tired, so they are unable to sleep and become sleep-deprived.

Researchers developed the hypothesis, that Alzheimer’s patients had trouble staying awake, after discovering a set of neurons that keep us awake and that are affected in Alzheimer’s from the start of the disease.

Joseph Oh, a medical student and one of the lead authors, said: “You can think of this system as a switch with wake-promoting neurons and sleep-promoting neurons, each tied to neurons controlling circadian rhythms.

“Finally, with this post-mortem tissue, we’ve been able to confirm that this switch, which is known to exist in model animals, also exists in humans and governs our sleep and awake cycles.”

Christine Walsh, the study’s other lead author, said she expects the research to lead to new ways of treating sleep disturbances driven by neurodegeneration.

She explained that treatments for Alzheimer’s could be adjusted depending on the patient’s needs, bumping up the “awake” system while tamping down the “sleep” system.

The findings are published in the JAMA Neurology journal.

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