Coffee, energy-shots and sugar drinks are faithful companions for those who cannot afford to sleep the required seven to nine hours a day. It is quite common for those with busy lifestyles to try to cheat sleep. But why do we need sleep to begin with? Taking up roughly 1/3 of our lives, sleep has been an intriguing phenomenon to scientists and philosophers alike ever since the late 400s BC.
Alcmaeon, an early Greek philosopher and scientist came up with the first known theory of sleep. He postulated that during sleep, the body would withdraw blood from the surface of the and circulate it to deeper vessels. From here, many theories unfurled including the three most popular today: the Evolutionary Theory, Information Consolidation Theory and the Repair and Restoration Theory.
The Evolutionary theory of sleep revolves around the idea of energy conservation. As seen with the placement of different species in food chains, those species with a less threatened existence appear to sleep more than those in constant danger.
The Information Consolidation Theory concentrates on the need of sleep to process information and thoughts, as well as the storing of memories. Finally, as recently emphasized by the The Nedergaard Lab in University of Rochester Medical Center, the Repair and Restoration theory states that sleep is essential for mental and physiological renewal and repair.
Sleep deprivation has been known to cause adverse manifestations on the human body, ranging from depression and cognitive impairment to diabetes and dementia. Evidently, sleep is considered a restorative necessity for humans. Maiken Nedergaard, at the School of Medicine and Dentistry at the University of Rochester Medical Center and her colleagues have unearthed a mechanism that further explains how.
The team began the study by observing mice brains in different states of consciousness. The experimental procedure involved tracing of the interstitial and cerebrospinal fluids through interstitial (intercellular) space. Together, cerebrospinal fluid (CSF) and interstitial fluid normally circulate the brain, taking care of any toxins that must be removed or degraded to maintain correct brain functioning.
By watching these dyes trail through the brain, the researchers discovered a phenomenon that was previously undetected. When anesthetized or sleeping, mice displayed a substantial increase of CSF flow throughout their brain and that sleep and anesthesia are correlated with an astounding 60% expansion of interstitial space as opposed to that of alert and awake mice.
This seems to indicate that the brain increases the number of routes dedicated to cleansing the brain during sleep.
Considering brain cells are highly affected by their environment, there needs to be a way to quickly rid the interstitial area of any possible synaptic (cell-cell communication) hindrances. Since the brain has no lymphatic system to filter out toxins, cerebrospinal fluid and interstitial fluid must move through the brain to perform the task.
Toxins around the brain accumulate as the day progresses, and the unconscious, asleep or anesthetized brain allows for an increase in CSF flow through tissues. CSF then diffuses toxins into the blood to be degraded by the liver. Without this improved “glymphatic” system, proteins related to Alzheimer’s and dementia accumulate in the brain.
The interstitial change from 13-15% to 22-24% between awake mice and sleeping/anesthetized mice sparked interest especially in the glia biology field. Glia cells are part of the connective tissue that supports the brain, and Nedergaard explored the possibility of cells having dual-identities.
“I think it is really interesting that glia appears to have two states, one during sleep where the work as a syncytium working on global cleaning of the brain and another state during wakefulness where they support local synaptic transmission,” Nedergaard wrote in an email to The News-Letter.
There appears to be a necessary choice to be made by the brain; it can either clean up after itself or keep working.
Such a discovery opens the way for many other questions. Does this change in conscious state alter the way neurons and their helpers work? Do neurotransmitters, and neuromodulators suffer any consequences as a result of sleep or lack thereof? Or even more intriguing, can such a substantial change in the brain be somehow correlated to consciousness?
“I think it is too preliminary to speculate on the mystery of consciousness, but our data add an entirely new aspects to the questions,” Nedergaard said.
As for our faithful companions, substances in coffee have been known to diminish the chances of attaining Alzheimer’s. Interestingly enough, the mechanism of action works through the modulation of the release of some of the same toxins relieved through “sleep cleansing.”
Hopefully, this can be a call to society to replace sleep as a priority in our busy, busy lives.