Why thinking hard makes people tired?

"New research shows that prolonged, intense cognitive work causes potentially toxic byproducts to build up in the part of the brain known as the prefrontal cortex". (ScitechDaily.com/Mental Fatigue Is No Illusion: Scientists Figure Out Why Thinking Hard Makes You Tired)

There is the possibility that we are tired during cognitive thinking for two reasons. The brain needs to reload its neurotransmitters. And if the temperature in the brain is rising too high. Cognitive operations turn difficult when the temperature rises. Especially when this happens inside the brain. 

The high temperature inside the brain causes the control of enzymes and other chemical processes to turn difficult. When neurons work hard their metabolism turns high level. The products of the metabolism of hard-working neurons also accumulate in the brain when a person thinks hard. 

And brain needs to decrease its temperature low enough that it can effectively continue its cognitive thinking process. So our brain requires sleep and breaks too. 

Getting tired is the mark that the brain needs a little break. And during that break called "sleep", they will decrease their temperature and reload neurotransmitters.  

Researchers found that when a person thinks the toxic byproducts are accumulating in the brain area called the "prefrontal cortex". That thing might be one of the reasons why we are getting tired while we are sleeping hard. But other things are involved in that process. When a person does cognitive work neurons in the brain are changing data. And during that process, they are using neurotransmitters. 

Whenever a chemical neurotransmitter crosses the synaptic border between neurons the enzyme destroys that neurotransmitter and frees the receptor in the neuron for the new neurotransmitter. So when a person thinks cognitively the neurotransmitters can go to a low level, and then the brains need to rest. During sleep, brains are reloading their neurotransmitters. The use of brains in cognitive actions requires energy. 

When the temperature in the brain goes up, cognitive performance goes down. High temperature makes it hard to control the neurotransmitters, proteins, and especially enzymes. When the temperature inside the brain turns too high the cognitive work turns too hard. And then brains get a signal that they must take a brake. That means brains will get a signal that they must go to sleep so that they can reload their neurotransmitters and make the temperature inside the brain get lower. 

https://www.cambridgebrainsciences.com/more/articles/as-temperature-goes-up-cognitive-performance-goes-down

https://scitechdaily.com/mental-fatigue-is-no-illusion-scientists-figure-out-why-thinking-hard-makes-you-tired/

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