What causes our brain to get “tired” and lose focus when thinking hard for extended periods of time like studying or thinking through a difficult concept?

Question

What causes our brain to get “tired” and lose focus when thinking hard for extended periods of time like studying or thinking through a difficult concept?

In: 120

Answer 1

I’m very much not any kind of expert so take it with a grain of salt but I recall reading about some experiments suggesting that it is to do with glucose depletion, and eating some helps powering through