13 June 2024

Narrowing of the pupils indicated brain fatigue

Japanese researchers have shown, using the example of cyber athletes, that a decrease in pupil size can be considered a marker of brain fatigue - a decrease in cognitive functions on the background of prolonged mental activity. At the same time, the person himself may feel quite awake at this time.

Scientists from the University of Tsukuba and Niigata University of Health and Welfare (Japan) in their study, published in the journal Computers in Human Behaviour, asked the following questions: how can a modern person achieve a balance between his activity and maintaining good health? How do you know when you've reached your limit? And what about professional video gamers whose lives are moving from reality to cyberspace?

"Although recent studies have shown that cyber athletes have higher levels of physical activity, their health problems are due to prolonged sitting and poor diet. In addition, Internet gaming and addictive disorders are particularly pronounced in these young people. These negative aspects should be carefully considered, but they are not limited to cybersports and apply to all activities of the modern person in the "digital" space. Finding solutions to these health problems is therefore crucial to optimise new, 'digital' lifestyles," the researchers said.

They emphasised that cognitive fatigue - a decline in executive functions in the face of mental strain - is not only inevitable today, but is a key problem affecting our productivity. This condition provokes impairments in inhibitory function, decision-making ability, and concentration, leading to a drop in efficiency and an increased risk of accidents. But it remained unclear: do people really recognise brain fatigue while they are sitting in front of a computer, and does this perception correspond to their actual state?

Japanese scientists decided to test whether pupil diameter - recently proposed as a "neuronal index" reflecting the activity of the brain's ascending excitation system - could play a role as a marker of cognitive fatigue. To do this, they recruited 33 people aged 18 to 35, mostly male: 14 video game enthusiasts and 19 "hardcore" players of eFootball (a Japanese sports football simulator), including professional cyber athletes with titles and rankings.

Two to seven days before the control measurements, volunteers played eFootball for at least an hour a day. They also filled out questionnaires and underwent impedance analysis, which assesses a wide range of morphological and physiological parameters of the body. In the run-up to the experiment, the participants were not allowed to consume alcohol, caffeine or exercise.

Already in the laboratory, the subjects, who were wearing heart rate monitors, had to play a football simulator for three hours, either alone or in pairs. Three times an hour they drank fresh water, 400-500 millilitres each. Meanwhile, the researchers recorded the subjective feelings of the participants, monitored mood (pleasure and fatigue) and executive functions, heart rate, collected saliva to assess the level of cortisol - one of the markers of fatigue and stress.

In addition, the scientists measured the diameter of the participants' pupils using an eye tracker equipped with an infrared camera. At the end of the experiment, everyone was paid 5000 yen (approximately 2800 rubles).

As the data analysis showed, regardless of the participant's experience, pupil diameter decreased after more than two hours of play. Meanwhile, heart rate did not change significantly, and cortisol levels were higher in the "hardcore" players than in the other subjects and dropped over time.

Pupils constricted during prolonged sessions, independent of autonomic nervous system activity and/or stress response. This implies a possible deactivation of the ascending arousal system and prefrontal cortex," the scientists said.

They noted that pupil constriction indicated cognitive fatigue regardless of how the participants - both professionals and amateurs - rated their condition. Probably, the point is that players, unlike ordinary office workers, experience pleasure from the process itself, which "overshadows" the feeling of fatigue. Secondly, the low "physicality" of cyber sports could play a role: dynamic movements of the whole body are not required here.

"However, cognitive decline can also occur without muscle (peripheral) fatigue. Our results showed a decline in executive function and a decrease in pupil diameter during prolonged cybersport activities - suggesting that cognitive fatigue is associated with brain deactivation independent of peripheral fatigue. Consequently, fatigue associated with reduced mental function is difficult to experience during cognitive tasks such as virtual football matches. This implies a role of corporeality in the embodiment of the feeling of fatigue," the authors of the research paper summarised.

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