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

Not an expert; there is some kind of „waste“ chemical that is building up when your brain is used. In our sleep this „waste“ is flushed out which is why after waking up it’s like a „reset“.