Focus performance diminishes after approximately 90 to 120 minutes due to neuronal circuits becoming less engaged.

“What you're entraining to is the release of particular neurochemicals, in this case, acetylcholine and dopamine that allow your brain to focus for particular periods of time, 90 minutes or so, and after about 90 minutes or so, the amount of those chemicals that can be released tends to drop very low, which is why your ability to focus becomes diminished.”

“What you can't negotiate, however, is that at about 100 minutes or 120 minutes, no matter who you are, you're going to see a diminishment in performance. You're not going to focus as well. And that's again because of the way that these 90-minute cycles are linked to the ability of the neurons that release acetylcholine and dopamine and to some extent norepinephrine, the things that give us narrow focus, motivation, and drive. the way that these 90-minute cycles are involved in those circuits. After about 90 minutes, those circuits are far less willing to engage, and therefore, it's much harder to continue to focus to a high degree.”