Current Biology: Why does using your brain make you tired?

Everyone's physical strength is limited, and physical labor beyond a certain level will make people feel exhausted and have to take a break to recove.

Likewise, mental work can be tiring, and a test of several hours is often exhaustin.

These may seem like common sense, but scientists still know little about the biology behind the.

On August 11, 2022, researchers from the Pitié-Salpêtrière Hospital in Paris and the Paris Brain Institute published a study entitled: A neuro-metabolic account of why daylong cognitive work alters the control of economic decisions in the Cell sub-journal Current Biology thesi.

The study suggests that cognitive fatigue may be due to metabolic changes in the brai.

Three years ago, research by Mathias Pessiglione's team, also published in Current Biology, showed that excessive exercise can also lead to mental fatigue, causing a decrease in activity including in the prefrontal cortex of the brain, an area critical for decision-makin.

According to Mathias Pessiglione, the influential theory is that fatigue is an illusion created by the brain that makes us stop what we're doing in favor of something more pleasurabl.

Work that involves a lot of thinking requires the brain to repeatedly resist the temptation of the opposite: do something less demandin.

To find evidence, in the new study, the researchers recruited 40 participants and divided them into two groups: a difficult group and an easy grou.

At three stages during the task, the researchers used magnetic resonance spectroscopy (MRS) to quantify metabolites in neural tissu.

They found that over time, participants in the difficulty group accumulated higher levels of glutamate in the prefrontal cortex of their brain.

It is well known that glutamate is the major excitatory neurotransmitter in the brain, and for normal cortical function it must be closely balanced with inhibitory neurotransmissio.

The researchers also measured pupils in both groups, and over time, participants in the difficult group had less pupil dilation, a measure of fatigue and cognitive effort, meaning they were more fatigue.

In addition to objective performance, participants were asked to rate their subjective fatigue levels on a rating scal.

The researchers believe this means that people may not be very good at listening to their bodie.

Combined with fMRI data from previous studies, these results support a neurometabolic model in which accumulation of glutamate triggers a regulatory mechanism that makes activation more expensive in the lateral prefrontal corte.

So, are there some ways to get around the limitations of our ability to think hard?

Mathias Pessiglione believes that there is no other way than rest and slee.
Because there is good evidence that glutamate disappears from synapses during slee.
Additionally, monitoring metabolites in the prefrontal cortex could help detect severe mental fatigu.
This method can help adjust your work schedule to avoid burnou.

He also suggested that people should avoid making important decisions when they are tire.

The research team says further work will shed light on the causal link between excess glutamate and mental fatigue, rather than just a link between the tw.

Original source:

Antonius Wiehler, et a.
A neuro-metabolic account of why daylong cognitive work alters the control of economic decision.
Current Biology, 202