A study published in Current Biology found that participants who spent > 6 hours working on a mentally taxing task had higher levels of glutamate.

Glutamate is an excitatory neurotransmitter that is important to memory, cognition, and mood regulation.

Too much of it, and it disrupts your brain function, a rest period can restore proper regulation of the molecule.

They used a technique called magnetic resonance spectroscopy to measure levels of glutamate in the lateral prefrontal cortex (LPFC)

The LPFC is the home of cognitive control. "If you get stung by something and want to scratch it", that's cognitive control. It's also the system that we reuly on to choose tempting short-term rewards, such as opting for snacks instead of health meals, over long-term gains.

For people who accumulated more glutamate in this region, they were more likely to not delay gratification, and choose smaller, short-term rewards.

Now that we have a system to measure metabolic changes in response to mental fatigue, this paves the way to future researchers to explore cognitive fatigue.

However, researchers still have to learn how to recover from mental exhaustion, specifically, how to restore glutamate levels.

Does sleep help? How long do breaks need to be to have a net effect?

These studies can help workers recover from high-stakes mental work such as air-traffic control.