Fatigue is an unavoidable physiological condition that cannot be overridden. A good night’s sleep is always desirable to start the day fatigue-free, but fatigue also builds up during the day.
Thinking, especially conscious thinking, generates certain ‘waste’ products (adenosine mainly) that hinder normal electrochemical activity in the brain. When the mind works hard for a sustained period it generates more wastes than can be diffused away, and this progressively hinders the firing of neurons in our neural networks, manifesting itself in the ‘brain fog’ feeling that we get. One of the effects of this waste accumulation is the reduced ability to concentrate on a task, which is when many incidents take place. The afternoon nap (especially popular in southern European and some Latin American countries) or the recommended ‘power nap’ may be ways that we can ‘buy time’ for our diffusion process to catch up with the build-up of wastes before overnight sleep comes around.
Research at the University of Groningen assessed the effect of mental fatigue on our ability to be attentive (Boksem, Meijmen and Lorist, 2005). The research found that, when driving a car while mildly fatigued, the driver’s ability to:
focus on the road and other vehicles (goal-directed attention) was diminished
operate the car (stimulus-directed attention) was not affected.
In other words, because the activity of driving (operating the car) is not inhibited while we are mildly fatigued, we think that we are paying as much attention as we normally do and this is ‘enough’ to drive safely, when in fact, this is unlikely to be the case.