A study recently published in the Proceedings of the National Academy of Sciences (PNAS) may reveal the answer. In this study, researchers kept people awake all night and measured levels of beta amyloid in the participants’ brains the next day. They then compared these levels to the beta amyloid levels in the same subjects’ brains after they had had a full night of sleep. Researchers found that a single night without sleep causes an increase in the amount of beta amyloid in the human brain. This indicates that poor sleep is likely an important risk factor for the development of Alzheimer’s.

So how were scientists in this study able to measure levels of beta amyloid, a microscopic protein fragment, in the brains of living humans? When doctors need to measure proteins in other tissues like skin, muscles, liver, etc., they simply biopsy a tiny piece of the tissue, usually with little risk to the patient. However, the brain is extremely sensitive, so it is very dangerous to perform a brain biopsy. Any bleeding or swelling in the brain could cause the patient to have a seizure or go into a coma, so a brain biopsy would never be allowed in an experiment. Brain biopsies are generally only used when doctors suspect the patient has a life-threatening condition. So for much of history, scientists who wanted to study proteins in the human brain needed to wait for someone to die and donate their brain to science.