The interruption of the sleep-wake cycle is a well-known symptom of Alzheimer's disease, but recent research suggests that an unorganized biological clock may also play a key role in neurodegenerative diseases.
Examining the role of circadian rhythm in the development of Alzheimer's disease and other forms of dementia is one of the wealth of insights presented this week at Neuroscience 2018, the annual meeting of the Society for Neuroscience at the San Diego Convention Center.
On Monday morning, Brian Lananna, a researcher at Washington University, St. Louis, presented preliminary results showing how muted the circadian rhythms at the cellular level can harm neurons, the brain cells responsible for human perception.
Researchers worked in petri dishes and mice and deactivated genes in astrocytes, the star-shaped cells that support neurons, thereby stopping the production of a key protein that, when dehydrated, led to an increase in damaging inflammation.
These results raise a fascinating question: Does a circadian rhythm cause Alzheimer's disease?
Lananna probably did not say. There are many other patterns in the game where many hypotheses involved building other proteins that lead to a devastating amount of memory loss over time.
But it's possible, Lananna said, that a malfunctioning biological clock is speeding up a process that's already underway.
"There is much evidence, though not clear – that inflammation can be a driver in Alzheimer's disease," said Lananna. "It's possible that if someone already has Alzheimer's, the increase in inflammation caused by circadian disorders could trigger the person over the edge or speeding up progress."
Further studies are looking at the key protein levels in Alzheimer's disease and compared the results with those who do not have the disease. A deeper study could eventually lead to medications that could be used to compensate for when circadian rhythms are out of sync.
The results are based on an increasing body of evidence that serious consequences exist for disrupting the circadian rhythm. Other studies have linked the ticking of the biological clock to a variety of health effects from heart disease to premature death.
Although this science is constantly evolving, researchers have increasingly recommended that the public get enough sleep, and having this in line with normal light-dark patterns in nature is likely to have a protective effect.
A significant boost in recent years has been the limitation of night time, which some studies have shown can affect normal sleep patterns.
Sleep quality is another area of research.
In general, deep sleep has proven to be the most beneficial type of sleep, and several essays on Neuroscience 2018 supported this idea.
The Walter Reed Army Institute of Research studied over-challenged soldiers and found that this type of trauma correlated with a significant reduction in each participant's deep sleep each night. A Walter Reed study had previously troubled soldiers undergo 40 hours of sleep deprivation to see if their performance was compromised or not.
Such a long stretch without sleep, said Cpt. Allison Brager, a researcher of Walter Reed, was created to simulate modern warfare when many soldiers have to operate in the dark and missions can go beyond 24 hours.
"We are really proud to own the night, and the consequences of staying overnight are that you need to sleep and you shift your sleep patterns to get the upper hand," said Brager.
The results of the study showed that soldiers who recently had a concussion were about 100 milliseconds slower than those who had not stopped after 40 hours of sleep deprivation. While a response time of less than a second does not seem to be much for a civilian, Brager said that she spoke for herself and not for the US military, that part of the time in combat could be a crucial decision.
"Living fire can be the difference between life and death," said Brager.
According to Eti Ben Simon of UC Berkeley's Center for Human Sleep Science, it has also been shown that deep sleep has no effect on emotional regulation.
Researchers at the center examined 18 healthy participants who were examined before and after an eight-hour evening phase, half of which was asleep and half of which were without sleep. For those who had no deep sleep, anxiety levels increased significantly, and brain imaging showed greater activity in the emotion-producing regions of the brain and also in the prefrontal regions, which normally suppress anxiety.
Having eight full hours of sleep per night seems to be a good anti-anxiety medicine.
"If we are chronically deprived of sleep and you continue to lose sleep, it could sensitize us to a higher level of anxiety and the development of an anxiety disorder," said Ben Simon.