By Wenle from Aofei Quantum Bit | Official Account QbitAI

Staying up late may make you dumber, and there is further scientific evidence to support this!

The physiological mechanism behind being easily distracted during the day after a lack of rest has been found: being 'brainwashed'.

A new study from MIT has revealed the internal changes in the brain during this moment. The study found that when attention is briefly lost, a wave of cerebrospinal fluid (CSF), which can be understood as the cleaning fluid in the brain, flows out of

This brainwashing process usually occurs during sleep to clean up waste accumulated during the day. In people who are sleep deprived, this nighttime-limited activity will start during the day when they are awake - at the cost of severe impairment in

The research has been published in a Nature sub-journal.

This study has caused widespread discussion among netizens. Some people mentioned that they feel very energetic after taking a daytime nap, possibly because their minds have been "washed" during this time.

However, the claim that staying up late will make you slower is not just a scare tactic. Actually, it is supported by scientific evidence before this statement.

Nighttime sleep is the best time for brain wash

In 2019, a research team at Boston University published a groundbreaking study in the journal Science. For the first time, they clearly captured the entire process of brain cleaning during human sleep through synchronized monitoring of functional mag

In the brain, there will be large periodic fluctuations in blood oxygen level-dependent signals. Red blood will flow out of the cerebral cortex on a large and periodic scale, and at this time, blue cerebrospinal fluid will take the opportunity to rap

One of them is β-amyloid, which is closely related to Alzheimer's disease.

△ Green indicates blood oxygenation signal, while purple indicates cerebrospinal fluid signal

After waking up, the cycle is gone, and cerebrospinal fluid can no longer rush into the brain in large quantities to complete effective cleaning.

Why can the cleaning mechanism of "blood withdrawing and cerebrospinal fluid entering" only be activated during sleep?

Through monitoring 13 volunteers, the research team found the answer.

During sleep, neurons in the brain enter synchronized rhythmic activity (manifested as slow-wave activity recorded by the EEG), and a large number of neurons stop exciting at the same time, and the demand for oxygen and glucose decreases, so that blo

So, the netizens said, "It's really correct to just wash up and go to bed." (doge)

The progress at Boston University indicates that slow wave loss, which usually reflects deep sleep, brain function suppression, or pathological conditions, is related to decreased cerebrospinal fluid flow.

What is more noteworthy is that increasing the total amount of cerebrospinal fluid, which is emphasized in 'washing the brain', could be an effective solution for preventing dementia in the elderly.

According to the latest research from MIT, if there is insufficient nighttime sleep, the cerebrospinal fluid cannot complete its cleaning, leading to affected concentration during the day.

Daytime wandering is being brainwashed

The team recruited 26 healthy volunteers to participate in experiments with adequate and insufficient sleep conditions separately.)

Volunteers are required to complete visual and auditory attention tests in two states. For example, in visual tasks, they need to closely watch a fixed cross on the screen and quickly press a button when it turns into a square; in auditory tasks, the

During the experiment, researchers simultaneously monitored the brain's electrical signals of volunteers, measured their brain's blood oxygen saturation and cerebrospinal fluid flow. They also recorded physiological indicators such as heart rate, res

Volunteers who were sleep-deprived performed significantly worse on tasks, showing longer reaction times and even failing to respond to screen changes or target sounds in some cases, leading to a state of mind wandering and space-out.

The more critical discovery is the internal changes in the brain. When volunteers lack concentration due to insufficient sleep, cerebrospinal fluid will flow out abnormally; when attention is restored, cerebrospinal fluid will flow back.

Moreover, this process is accompanied by synchronous physiological changes. During mind wandering, breathing and heart rate decrease, and the pupils begin to contract about 12 seconds before cerebrospinal fluid flows out, and gradually expand again a

Based on experimental data, researchers speculate that this is the malfunction of the brain during daytime.

Under normal circumstances, the brain will initiate the cleaning process during deep sleep, when cerebrospinal fluid flows regularly to clear metabolic waste accumulated during the day, maintaining the normal function of the brain.

When there is insufficient sleep, this cleaning process cannot fully occur, leading to the accumulation of waste products in the brain. At this point, the brain will seek alternative means to clean itself - forcefully initiating a cerebrospinal fluid

Although this operation can remove waste to some extent, it comes with a cost of occupying the neural resources required to maintain attention, ultimately leading to a decrease in attention span.

Even when people are awake, they have to forcibly initiate a sleep-mode clean, which takes up the energy originally used to maintain attention, leading to mind wandering.

In addition, research also speculates that there may be a master switch in the brain that controls both our attention and physical responses such as cerebrospinal fluid flow, heartbeat, and respiration. A substance called norepinephrine in the brain

The primary author of this study is computational neuroscientist Zinong Yang who focuses on the dynamics of the brain in different states of attention.

She earned her bachelor's degree in cognitive science at the University of Santiago and later received her PhD at Boston University and Massachusetts Institute of Technology, under the guidance of Laura D. Lewis.

Both studies are from Lewis Lab with the corresponding authors being Laura D. Lewis.

△Left: Zinong Yang Right: Laura D. Lewis

Therefore, situations such as swiping your mobile phone to check information and suddenly forgetting what you want to search for while swiping your fingers may not be simply a lack of energy, but the brain is starting a brainwashing program "violatin

We suggest not staying up late unless necessary in the future.

[1]https://www.nature.com/articles/s41593-025-02098-8[2]https://news.mit.edu/2025/your-brain-without-sleep-1029[3]https://news.ycombinator.com/item?id=45771636[4]https://science.sciencemag.org/content/366/6465/628

— End —