The brain may make worse decisions when it is tired

Tam-Tri Le, Phenikaa University (Hanoi, Vietnam)
https://orcid.org/0000-0003-3384-4827

September 5, 2022

It is easy to feel muscle fatigue after a hard session in the gym, and the body just wants to relax and recover. But how about brain fatigue? Cognitive activity can also appear to be “lazier” after a long time of thinking hard.

The brain works all the time, including when we sleep. But like any other organ, it cannot exceed physical and energy constraints. Laziness in thinking may be caused by a lack of strength of will. However, it becomes a biological problem when the brain gets physically tired. A recent study published in Current Biology examines the connection between neurometabolic issues and decision-making [1].

In the study, researchers found that people who performed high-demand cognitive control tasks afterward would be more likely to choose immediately gratifying smaller rewards. On the other hand, those who performed low-demand cognitive control tasks would later tend to have more impulse control for choosing higher rewards with delayed gratification.


Tired, by Takashi Hososhima (CC BY 2.0); https://commons.wikimedia.org/wiki/File:Tired_(8991770030).jpg

The researchers used magnetic resonance spectroscopy to monitor brain metabolites throughout the study. Hard cognitive work results in glutamate accumulation in the lateral prefrontal cortex. The accumulation of glutamate triggers a regulation mechanism that makes it more costly to activate the lateral prefrontal cortex, thus making cognitive control harder. This mechanism is to protect the integrity of brain functioning in the long term [2]. For example, it prevents the accumulation of noxious substances to dangerous levels.

It is apparent that the human brain is an information processing system that is optimized based on its biological components and energy constraints. Therefore, thinking is also subject to (and self-adjusts in alignment with) the biochemical principles of physiology [3]. Next time you need to make an important decision, make sure that the brain is not already exhausted from a hard day at work.

References

[1] Wiehler A, et al. (2022). A neuro-metabolic account of why daylong cognitive work alters the control of economic decisions. Current Biology, 32(16), 3564-3575.e5. https://doi.org/10.1016/j.cub.2022.07.010

[2] Holcombe M. (2022, August 11). Your body may be pushing you to make worse choices after a day of hard thinking, study finds. CNN. https://www.cnn.com/2022/08/11/health/cognitive-fatigue-study-wellness/index.html

[3] Vuong QH. (2022). Mindsponge Theory. https://books.google.com/books?id=OSiGEAAAQBAJ