The method by which this area was found to be critical is particularly interesting.

FTA:

Saper analyzed a dataset of almost 1,000 subjects who had entered into a memory and aging study back in 1997, when they were all healthy 65-year-olds. As part of the study, they had all agreed to wear a small watch-sized device on their wrists for about 7 to 10 days, every two years, that would record all their movements. Upon their deaths, their brains were donated to science, so research could continue.

Saper chose 45 brains to examine, based on whether or not the ventrolateral preoptic nucleus was still intact. First he stained the brain in order to find the cluster of neurons, which were located in a similar part of the human brain as the rats' brains.

Then he linked the neurons found in the brain to the rest-activity behavior data collected in that person’s final year of life. He found that the fewer neurons one had, the more sleep fragmentation that person experienced in the last year of life. Brains with the largest amount of neurons (over 6,000) belonged to people with longer, uninterrupted sleep.

Another key finding from the study: The link between fewer neurons and less sleep was even more pronounced in people who had died with Alzheimer’s disease.