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Why does hard thinking make us tired?

Researchers were quick to point out that there are no quick fix solutions for this limitation of the brain.

You might have noticed that on Occasions when you think hard about something, you end up feeling tired. You are able to understand when this happens after hard physical labour, but you are surprised when this happens after hard thinking as well. Rather than try to find why this happens, you would have most likely let it pass, trying to give yourself some rest as you already feel exhausted.

Researchers from the Pitie-Salpetriere University in Paris have probed this very question as to why intense cognitive thinking makes us feel mentally exhausted. Their results were reported in Current Biology on August 11. Brains, as opposed to machines, can’t compute continuously. The researchers set out to understand what mental fatigue really is. They suspected the brain’s need to release potentially toxic substances built-up from neural activity as the reason for tiredness and decided to look for evidence.

Brain chemistry monitored

Using magnetic resonance spectroscopy, they monitored the brain chemistry of two groups of people over the course of a day. While one group needed to think hard, the other had relatively easier cognitive tasks. The group doing hard mental labour showed signs of fatigue, including reduced pupil dilation. In technical terms, people in this group had higher levels of glutamate in synapses of the brain’s prefrontal cortex.

Glutamate accumulation

Along with existing evidence, this supports the idea that further activation of the prefrontal cortex becomes more costly following glutamate accumulation. In effect, a mentally tough workday eventually leads to cognitive control becoming more difficult. Researchers were quick to point out that there are no quick fix solutions for this limitation of the brain. Rest and sleep is what is suggested as there is evidence to show that glutamate is eliminated from synapses during sleep.

Scope for future studies on the subject includes learning why the prefrontal cortex is particularly susceptible to glutamate accumulation and fatigue. Researchers believe that learning more about the markers of fatigue in the brain could help us plan our lives to avoid burnout, and may even predict recovery from health conditions like depression or cancer.

Picture Credit : Google

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