He mental fatiguean experience that affects millions of people around the world, has acquired new scientific relevance after the COVID-19 pandemic.
Researchers from various disciplines are making progress in understanding the biological roots of mental fatigue, a phenomenon that not only reduces motivation and ability to concentratebut can also have serious consequences on daily life and public health.
According to Naturethese advances open the door to better measurement and treatment methods, especially for those suffering from debilitating disorders like long COVID.
Mental fatigue, also known as cognitive fatiguemanifests itself as a progressive decrease in the ability to maintain control and regulation of thought. This phenomenon can appear after long work days, school days or constant decision making., and affects both healthy people and those suffering from chronic diseases.
According to Mathias Pessiglionedirector of research at the Paris Brain Institute, mental fatigue arises when the brain abandons automated routines and faces new situations that require sustained cognitive effort.
According to Naturethis type of fatigue acts as a physiological warning signalindicating that the brain is approaching its limits and needs rest.
Over the past five years, research into mental fatigue has seen notable momentum, in part due to the rise in cases of long COVID. Scientists such as Pessiglione, Vikram Chib of Johns Hopkins University and Clay Holroyd of Ghent University have explored various theories about the biological causes of this phenomenon.
One of the most accepted hypotheses suggests that Mental fatigue is related to metabolic changes in brain regions responsible for cognitive control. Possible links have been identified with metabolites such as glucose and lactate, neurotransmitters such as glutamate and adenosine, and proteins such as brain-derived neurotrophic factor.
Even protein fragments associated with Alzheimer’slike the beta-amyloidcould contribute to the problem by interfering with glutamate clearance or increasing neuroinflammation.
Holroyd defends the theory of “toxic accumulation”which compares fatigue with pain as body protection mechanisms. Although the feeling of tiredness can be temporarily ignored, the brain has automatic systems that force rest, and deep sleep is essential to eliminate metabolic waste and restore energy balance.
Measuring mental fatigue remains a challenge for neuroscience. Traditionally, subjective self-reports or performance tests on working memory tasks have been used. However, these methods have important limitations.
According to Daniel Forgerresearcher at the University of Michigan cited by Nature“people are terrible at evaluating their own fatigueFactors such as motivation, boredom or frustration can distort results, and training can mask real fatigue.
To overcome these limitations, researchers are developing new strategies that combine biochemical analysis with the assessment of motivation and decision making. A study led by Pessiglione in 2022 showed that after performing demanding cognitive tasks, participants tended to prefer immediate rewards over greater long-term benefits.
This behavior was associated with greater glutamate accumulation in the lateral prefrontal cortex, a key region for working memory and decision making. Besides, Matthew Appsfrom the University of Birmingham, highlights the role of dopaminewhich, when it decreases after sustained effort, reduces the willingness to invest mental energy.
Scientific interest in mental fatigue has intensified in recent years due to its central role in long-term COVID. As Chib noted in statements cited by Naturefatigue appears as the predominant symptom of this condition.
This symptom is also common in myalgic encephalomyelitis (chronic fatigue syndrome), post-traumatic stress disorder, multiple sclerosis, depression and Parkinson’s disease. Additionally, extreme fatigue can appear after cancer treatments, brain injuries, strokes, or exposure to toxins.
Research suggests that individual differences in brain chemistry could explain why some people experience chronic or extreme fatigue. In these cases, simple mental tasks can be as overwhelming as brain surgery, highlighting the seriousness of the problem.
The impact of mental fatigue transcends the clinical setting and profoundly affects daily life. Ana Lia Tamariza Miami-based artist and health coach diagnosed with myalgic encephalomyelitis, describes the difficulty of separating mental from physical fatigue.
“Sometimes, I can’t read another word,” he says in Nature. For her, Any task that requires concentration can leave you physically exhausted, and physical exertion can exhaust your mind.. This experience illustrates how mental and physical fatigue can be interrelated and share biological mechanisms.
Research supports this interaction. Apps points out that, after running a marathon, physical exhaustion is accompanied by intense mental fatigue due to the concentration required. Conversely, Chib and his team have observed that, after demanding cognitive tasks, even healthy people show a lower willingness to exert physical effort.
The development of better methods to measure mental fatigue and understand its biological mechanisms is a priority for the scientific community. Deep sleep is emerging as a key element in brain recoveryby facilitating the elimination of metabolic waste and the restoration of neuronal circuits.
Additionally, the roles of stress, circadian rhythms, and inflammation in the onset and persistence of cognitive fatigue are being investigated.
According to Naturethe identification of brain biomarkers and the integration of innovative experimental approaches could pave the way to more effective treatments for those suffering from mental fatigue, whether occasional or chronic.
The magnitude of the problem and the urgency of finding effective solutions drive researchers to delve deeper into this field. Deciphering the mechanisms of mental fatigue is essential to advance its study and the development of interventions that improve the quality of life of millions of people.
