Your brain has a decision center, the region right behind your forehead. Sustained mental work causes a chemical called glutamate to build up there.
As it accumulates, your brain starts throttling that region to protect itself. The result: you shift toward lazy, impulsive choices.
A 2022 study watched this in real time with brain scans. People doing cognitively hard work had measurably more glutamate in that region by afternoon, and made measurably worse decisions as a result.
The numbers are hard to ignore
Researchers tracked all Danish public school children over four years and found test scores dropped 0.9% for every hour later in the day a test was taken.
A 20-minute break significantly restored performance.
Doctors prescribed more unnecessary antibiotics the further into their shift they got. Not because they stopped caring, but because their brains were depleted.
Three fixes that actually work
1. Front-load your hardest decisions. Your decision center is freshest in the first 2-3 hours after waking. Don't spend that window on email and Slack.
2. Reduce how many decisions you make. The fewer low-stakes choices you face daily, same outfit, same lunch, same routine, the more brain power stays available for the ones that matter. People were 10x more likely to buy when given 6 options instead of 24.
3. Take a real break. Not scrolling. Eyes closed, 15-20 minutes. Research shows this is enough to significantly restore performance.
One thing worth knowing on the supplement side
Two nutrients directly support the decision region of your brain.
Citicoline increased brain energy by 14% in the frontal region in a brain imaging study.
Phosphatidylserine cut cortisol by up to 39%, the stress hormone that shuts that region down.
I use MLP. It stacks both in research-backed doses. Worth looking at if decision quality matters to your work.
🛠️ Tools & Resources
Oura Ring - I love this thing. it tracks your HRV and readiness score daily. Once you know your personal energy curve, you can schedule your most important decisions around it instead of guessing.
"When" by Daniel Pink - the clearest book I've read on how time of day shapes your brain's performance. Covers the afternoon trough, why certain hours are better for certain types of decisions, and how to build your day around it.
Mind Lab Pro - includes citicoline and phosphatidylserine, the two nutrients most directly linked to prefrontal function. I take it in the morning before deep work.
20-minute nap - no product needed. Block it in your calendar before 2pm. The research is clear: a real break beats more caffeine.
❤️ Thank you for reading. See you next Sunday.
—Ernest
Founder, Enhancing Brain