http://english.elpais.com/science-tech/2022-08-12/scientists-say-too-much-glutamate-is-why-thinking-hard-makes-you-tired.html
This is a topic I'm looking into. I've noticed that particularly frustrating jobs leave me completely exhausted within hours. It isn't the mental work itself, because learning a lot or working at a desk job which I enjoy doesn't do this. Wondering why only some types of mental effort (in my case, at least, only mental effort where I don't feel I'm making progress and which seems to go on interminably) are so unpleasant and require recuperation (usually a nap). Some theorize it isn't the glutamine itself, but buildup of by-products... But one way or another, something appears to need to be "cleared" before concentration which provokes the fatigue can be restored.
Forgive me for sharing if this isn't interesting to you guys. Give me some feedback. I'm becoming interested in supplementation of certain things like niacin (precursor to NAD in mitochondria), precursors to neurotransmitters (L-Dopa http://www.healthline.com/nutrition/how-to-increase-dopamine), etc. Certain things, like niacin, clearly make a difference in function in me. How about you?
----
Excerpt:
"To study why mental exercise can be as tiring as physical exercise, the French scientists had 50 people perform a series of tasks for 6.5 hours (the average workday in France). One group was asked to perform more complex tasks than the other, while the researchers studied their brains.
An eye-movement tracking system was used to record pupil dilation. Other studies have found that eyes stop moving and pupils dilate when the brain is performing a calculation or is in the final phase of decision-making. In addition, they used a brain-imaging technique (magnetic resonance spectroscopy) to measure activity in the prefrontal cortex, where the executive brain functions happen, and to identify the residuals produced by this activity. They also developed performance tests and questionnaires to subjectively measure the level of burnout.
“Glutamate is the main excitatory neurotransmitter in the brain; it’s found in many parts of the brain and is necessary for normal brain functions. We found that it increases during the performance of demanding mental tasks.”
Antonius Wiehler, ICM Paris Brain Institute (France)
Recently published in Current Biology, the study found clear differences between the two groups (high-demand cognitive control tasks and low-demand tasks). They only observed signs of fatigue, including less pupil dilation, in the high-demand group. As time passed, the high-demand group began asking for more immediate rewards for task completion. But the most convincing evidence was what they saw happening inside the brains of the subjects. Those in the high-demand group had higher levels of a molecule – glutamate – in the synapses (the electrochemical connection between nerve endings) of the lateral prefrontal cortex, the brain region responsible for cognitive control....
“Let’s say you have to go out to buy some bread, and just thinking about moving your body to do that makes you feel tired. Shortness of breath is not causing that feeling,” says Segura. “This has a lot to do with the brain regions where actions are planned, and with the need for glutamatergic transmission to function well for the action to happen. When glutamate, one of causes of brain damage in stroke victims, is insufficient, it can result in certain neurodegenerative diseases and may also produce the so-called neurological fatigue.”"
| 
