Behavioral tasks have been developed in neuroscience to assess the demand for cognitive control. These tasks, such as working memory and task-switching paradigms, can cause frequent remapping of stimulus-response associations based on contextual information. Functional neuroimaging studies using these paradigms have identified a lateral prefrontal-parietal system recruited when more cognitive control is required. However, it is unclear why exercising cognitive control is exhausting. There are various theories on thinking effect on the brain.
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According to resource depletion theories, exercising cognitive control may deplete the global energy supply (such as blood glucose). Although evidence for these theories has been subject to more research, empirical support remains lacking. These theories fail to explain what makes self-control unique and why other cognitive processes, such as vision, would not cause (or be affected by) global resource depletion.
To reconcile the functional and biological accounts of cognitive fatigue, scientists propose that (1) such fatigue results from an increase in the cost of exerting cognitive control, and (2) this, in turn, results from metabolic changes in the brain system underpinning cognitive control.
Toxic accumulations of thought byproducts cause tiredness.
Behavioral sciences aim to understand the workings of the human brain. With varying theories of the effect of overthinking, scientists set out to examine new studies. The new findings show that when hard cognitive work happens for a long time, potentially toxic byproducts accumulate in the prefrontal cortex of the brain. According to the study, cognitive fatigue changes our control over decisions. The researchers suspected it was due to the need to recycle potentially toxic substances produced by neural activity.
The researchers studied two groups: those who had to use more cognitive energy and those who had relatively simple cognitive tasks. Only in the group doing hard work did they notice signs of fatigue, such as decreased pupil dilation. Those in the hard thinking group also exhibit a shift in their preferences toward options that promised rewards in a short period with little effort. They also had higher levels of glutamate in prefrontal cortex synapses, which was critical. Together with previous evidence, the scientists argue that glutamate accumulation makes further activation of the prefrontal cortex less likely, making cognitive control more difficult.
The current behavioral findings replicate and extend previous studies that exerting intense cognitive control, whether for intellectual work or endurance sport, causes fatigue, manifesting as a preference for immediate options without further thought.
Clinical significance
Monitoring prefrontal metabolites, for example, could aid in detecting severe mental fatigue, according to the researchers. Such a skill may help in adjusting work schedules to avoid burnout. With rising figures of mental health challenges caused by burnout, clinicians can advise their patients on the scientific dangers of overthinking and the potential for further brain damage.
Conclusion
Everybody gets tired when they overthink. For years, scientists have presented various theories as to why. The present study shows a new theory of toxic waste accumulation as the cause of brain fatigue. A tendency to choose the immediate option without further thinking due to this accumulation is more likely. The study also suggests that people avoid making important decisions when tired.
References
Wiehler, A., Branzoli, F., Adanyeguh, I., Mochel, F., & Pessiglione, M. (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
