Contrary to popular scientific theory, the brain’s ability to rid itself of toxins may actually be reduced during sleep. For the past decade, the leading explanation for why we sleep has been that it provides the brain with an opportunity to eliminate toxins. However, a new study by scientists at the UK Dementia Research Institute (UK DRI) at Imperial College London indicates that this may not be the case.
According to the researchers, the latest findings are surprising and more work is now needed to understand exactly what is happening and why. Their work is published in the journal Nature Neuroscience.
Does the brain eliminate toxins during sleep?
By measuring toxin elimination and fluid movement in the brains of mice, they showed that it was significantly reduced during rest and under anesthesia.
The researchers used a fluorescent dye, observing how quickly the dye moved from one area of the brain to another and was cleared from the brain. This allowed them to directly measure the rate of elimination of the dye from the brain. They found that clearance of the dye was reduced by about 30% in sleeping mice and 50% in mice under anesthesia, compared to mice kept awake.
Prior to this, the leading theory was that sleep enhances the elimination of toxins from the brain, which occurs through the glymphatic system (a mechanism that eliminates waste from the central nervous system). However, this has never been definitively confirmed, and previous studies relied on indirect means of measuring fluid flow through the brain.
Professor Nick Franks, professor of biophysics and anesthesia at Imperial College London and co-lead of the study, said: “The field has been so focused on the idea of elimination as one of the main reasons why we sleep, that we are were very surprised.” to observe the opposite in our results we found that the rate of clearance of the dye from the brain was significantly reduced in animals that were asleep or under anesthesia.
“We currently don’t know what slows the removal of molecules from the brain in these states. The next step in our research will be to try to understand why this happens.”
The size of molecules can affect how quickly they move through the brain, and some compounds are eliminated through different systems. Therefore, the extent to which the findings are generalizable is not yet confirmed.
Professor Bill Wisden, interim center director of the UK Dementia Research Institute at Imperial, and co-lead of the study, explained: “Although we have shown that eliminating toxins may not be a major reason for where we sleep, there is no denying that sleeping well is important.
“Interrupted night’s rest is a common symptom experienced by people living with dementia, however we do not yet know whether this is a consequence or a driving factor in the progression of the disease. It may be that having good sleep helps reduce the risk of dementia for reasons other than eliminating toxins.
“The other side of our study is that we showed that brain cleaning is highly efficient during the waking state. In general, being awake, active and exercising can more efficiently cleanse the brain of toxins.”
Next, the researchers aim to find out how sleeping well reduces the elimination of toxins from the brain in mice and to explore whether their findings are applicable to humans.
Sleep restores brain connections
During night’s rest, the brain weakens new connections between neurons that were forged during wakefulness, but only during the first half of the night’s rest, according to a new study in fish by UCL scientists.
The researchers say their findings, published in Nature, provide insight into the role of good sleep, but still leave an open question about what function the second half of a night’s rest serves.
The researchers say the study supports the synaptic homeostasis hypothesis, a key theory about the purpose of sleep that proposes that sleep acts as a reset for the brain.
Lead author Professor Jason Rihel (UCL Cell & Developmental Biology) said: “When we are awake, connections between brain cells become stronger and more complex. If this activity were to continue unabated, it would be energetically unsustainable. Too many active connections between brain cells could prevent new connections from being created the next day.
“Although the function of sleep remains mysterious, it may serve as an ‘off-line’ period in which such connections can be weakened in the brain, in preparation for learning new things the next day.”
For the study, the scientists used optically translucent zebrafish, with genes that allow them to easily visualize synapses (structures that communicate between brain cells). The research team monitored the fish during several sleep-wake cycles.
Researchers have found that brain cells gain more connections during waking hours and then lose them during sleep. They found that this depended on how much sleep pressure (sleep need) the animal had built up before it could rest; if the scientists deprived the fish of sleep for a few more hours, the connections continued to increase until the animal could sleep.
Professor Rihel added: “If the patterns we observed hold true in humans, our findings suggest that this remodeling of synapses may be less effective during a midday nap, when sleep pressure is still low, rather than during night, when we really need to sleep.” the sleep.”
The researchers also found that these rearrangements of connections between neurons occurred mainly in the first half of the animal’s nocturnal sleep. This reflects the pattern of slow-wave activity, which is part of the sleep cycle and is strongest at the beginning of the night.
First author Dr Anya Suppermpool (UCL Cell & Developmental Biology and UCL Ear Institute) said: “Our findings add weight to the theory that sleep serves to dampen connections within the brain, preparing for further learning and new connections the next day. But our study tells us nothing about what happens in the second half of the night.
“There are other theories that sleep is a time for eliminating waste in the brain or repairing damaged cells. Perhaps other functions come into play in the second half of the night.”
Sleep deprivation affects cognitive performance
Anyone who has ever slept poorly or not slept at all one night knows how much lack of sleep can affect your concentration the next day. Researchers at the Leibniz Research Center for Work Environment and Human Factors investigated how exactly sleep deprivation affects brain performance.
The results show that not only brain activation, but also the alteration of connections between neurons is affected by sleep deprivation. Both have a significant effect on memory performance and working memory.
Sufficient sleep is essential for optimal daytime performance. Lack of sleep not only impairs attention, but also memory and learning processes. To encode new memory contents, connections between neurons in the brain are strengthened or weakened during wakefulness. This process is called neuroplasticity. During sleep, relevant connections become further strengthened, while irrelevant ones weaken.
In case of sleep deprivation, this weakening of irrelevant connections does not occur. Cortical excitability remains increased, which leads to reduced signal transmission. New external stimuli and information can therefore be processed only poorly or not at all and learning becomes more difficult. This increased cortical excitability disturbs neuroplasticity. This means that overactive brain activity makes it harder for neurons to shape connections.
There is, however, a difference between complete sleep deprivation and working against your personal sleep and wakefulness phases (chronotype). In the latter, brain excitability and neuroplasticity are reduced during suboptimal hours of the day. In sleep deprivation, however, excitability increases. Especially in demanding activities, working according to your chronotype can improve work performance.
Since the brain’s plasticity and excitability depend on sleep, it could play a role in preventing cognitively impaired diseases. Examples of such diseases are Alzheimer’s disease, which is often accompanied by sleep disorders, and major depression.
With depression, brain activity and neuroplasticity are reduced, and this could be counteracted by sleep deprivation, a well-established antidepressant treatment.
#Sleep #eliminate #brain #toxins
