Despite desk jobs lacking any kind of physical rigor, the tiredness they can invoke is unmistakable. Research from the Paris Brain Institute explores why that might be. The study scanned the brains of volunteers at various points during the work day and found that tasks that require a high degree of concentration can result in the build-up of a chemical called glutamate, which can have toxic consequences.
This chemical is usually used to send signals from nerve cells to the brain, but when it appears in large quantities it can alter the performance of the lateral prefrontal cortex (lPFC), which is the part of the brain used for things like decision-making and planning.
Mental fatigue
The consequences of mental fatigue are well documented, and the study examines whether things like multitasking, problem-solving, and intense focus can tire out the lPFC, which in turn influences the effectiveness of our decisions. Do prolonged cognitive tasks influence the supply of nutrients to the brain?
They put volunteers through a range of computer-based tasks over a six-and-a-half-hour period to reflect a typical working day. One group had difficult tasks to perform, while the second group performed simpler tasks. In both groups, participants managed to achieve an 80% success rate.
The researchers used magnetic resonance spectroscopy (MRS) to see the impact on the brain and measure the levels of metabolites within it. Readings were taken at the start, the end, and the middle of the day.
The results showed that the high-demand group produced significant levels of fatigue markers, including glutamate. The build up of these toxic chemicals was found in the lateral prefrontal cortex, but not in other parts of the brain. What’s more in a subsequent test to measure decision-making, this group also preferred choices that were less mentally taxing and required less time to make.
A new structure
The findings shed a degree of doubt on whether our working days are structured in the most productive way. The results suggest we should be striving to do the most cognitively challenging tasks at the start of the day and hold off on making any important decisions later on.
It’s also clear that our decision-making might also benefit from regular rests. Indeed, when decisions are of critical importance, the researchers believe that compulsory rests might be required.
Next time you have to make a difficult decision at the end of a long day, be aware you will be inclined towards low-effort actions with short-term rewards. If possible you should sleep on it.
