AUG 24, 2022 8:00 AM PDT

Why is Thinking Hard So Exhausting?

WRITTEN BY: Kerry Charron

Trending phrases like “hustle culture” and “grind culture” imply that individuals will only be successful if they work non-stop, but a study indicates that brain rest is critical. A study published in Current Biology found that several hours of demanding cognitive activity cause toxic byproducts to accumulate in the prefrontal cortex. When this accumulation occurs, people gravitate to activities requiring less effort. 

The researchers hypothesized that this shift in cognitive activity is the brain’s effort to flush out toxins generated from intense neural activity. The study evaluated two groups of participants: those with more mentally challenging tasks and those with easier cognitive tasks. Magnetic resonance spectroscopy (MRS) was used to track participants’ brain chemistry over the course of a workday. The group assigned more challenging tasks showed fatigue and reduced pupil dilation, and they had higher glutamate levels in the synapses of the prefrontal cortex. Elevated glutamate levels negatively impact decision-making control.  

The shift to a less cognitively demanding activity may reflect the brain’s effort to recuperate from mental stress. According to study author Dr. Mathias Pessiglione of Pitié-Salpêtrière University, “Influential theories suggested that fatigue is a sort of illusion cooked up by the brain to make us stop whatever we are doing and turn to a more gratifying activity. But our findings show that cognitive work results in a true functional alteration—accumulation of noxious substances—so fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning.” Previous research has found that sleep facilitates the process of glutamate removal from the synapses. Therefore, sufficient rest and sleep is critical for recovery.  

A different study also found that quality and length of breaks from mental work are necessary for recovering from fatigue. The researchers analyzed participants’ sleep cycles, cortisol levels in saliva, and self-reported outcomes. Cortisol levels were significantly higher in those participants who experienced shorter rather than longer off-job hours. 

Monitoring glutamate accumulation levels in the prefrontal cortex can be used to detect and avoid extreme mental fatigue and prevent burnout. Future studies will focus on the role of the prefrontal cortex and why it is prone to glutamate accumulation and fatigue.  

Sources: Current Biology, Eureka News Alert 


About the Author
Bachelor's (BA/BS/Other)
Kerry Charron writes about medical cannabis research. She has experience working in a Florida cultivation center and has participated in advocacy efforts for medical cannabis.
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