Working sitting in an office or as a stocker in a supermarket, what is more tiring? That physical work can be exhausting no one doubts it, but he who demands a mental overexertion, although we are seated, it is not far behind either. Sitting down to think hard for hours also makes one feel crippled. And it has an explanation. A group of researchers has found new physiological evidence behind that feeling of being exhausted after intense intellectual work.
The results, published in the journal “Current Biology”, show that when vigorous cognitive work continues for several hours, it causes the accumulation of potentially toxic by-products in the prefrontal cortex of the brain. This alters your control over decisions, so you switch and tend to choose simple actions that don’t require effort or waiting as cognitive fatigue sets in, the researchers explain.
“Some influential theories once suggested that fatigue is a kind of illusion concocted by the brain to get us to stop what we’re doing and move on to a more rewarding activity. But our findings show that cognitive work results in a true functional impairmentthe accumulation of harmful substances, so fatigue would be a signal that makes us stop working, but with a different purpose: to preserve the integrity of the functioning of the brain«, explains Mathias Pessiglione, from the Pitié-Salpêtrière University in Paris ( France).
Pessiglione and his team wanted to understand what the mental fatigue. Why machines can calculate continuously and the brain cannot. They suspected that the reason had to do with the need to recycle potentially toxic substances arising from neural activity.
To prove it, they used magnetic resonance spectroscopy to monitor brain chemistry over the course of a working day. They looked at two groups of people: those who needed to think a lot and those who had relatively easier cognitive tasks.
They saw signs of fatigue, including reduced pupil dilation, only in the group that did hard work. These also showed in their choices a shift towards options that offered rewards in a short time and with little effort. They also had higher levels of glutamate at synapses in the prefrontal cortex of the brain. Together with the above evidence, the authors say this supports the idea that glutamate accumulation makes further activation of the prefrontal cortex more costly, so that maintaining cognitive control is more difficult after a day’s work mentally. Lasted.
Is there any way to bypass this limitation of our brain’s ability to think a lot? “Not really, I’m afraid,” says Pessiglione. However, the expert dares to give “a good recipe for life”: “Rest and sleep! There is good evidence that glutamate is cleared from synapses during sleep.”
There may be other practical implications. The researchers suggest that monitoring prefrontal metabolites could help detect severe mental fatigue, and this may help adjust work schedules to avoid reaching exhaustion. They also advise people not to take important decisions when they are tired.
In future studies, they hope to learn why the prefrontal cortex seems especially susceptible to glutamate buildup and fatigue. They are also curious whether the same fatigue markers in the brain could predict recovery from health problems, such as depression or cancer.