Anyone who has to concentrate for a long time gets tired of it. But why is that so? In a study in the journal ‘Current Biology’, French scientists now point to an abundance of the substance glutamate in the brain.
Glutamate is said to cause mental fatigue and people to make more impulsive decisions.
A French research team led by Antonius Wiehler measured the amount of substances in the brains of test subjects several times a day. There were two groups. One group was given complex tasks, while the other group had to perform relatively light cognitive work. The researchers concluded that when people think intensively for several hours, and therefore perform a lot of cognitive effort, glutamate builds up in the prefrontal cortex, the brain region behind the forehead that is active when people plan things or solve complex problems.
Glutamate is a so-called neurotransmitter. This is a signal substance that transmits nerve impulses between nerve cells and gland or muscle cells. The more cognitive effort, the more glutamate builds up in the brain.
But a build-up of glutamate causes mental fatigue, the researchers write. This, in turn, leads people to choose more relaxing activities that require little effort or patience.
Thinking therefore causes a change in the brain, the research shows. Since fatigue causes people to take a break, it is a means of ensuring the proper functioning of the brain.
However, the study also seems to be criticized. Neurophysicist Harald Möller (Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig) said that increases in the substance often occur when brain areas are stimulated, but that concentration decreases again when the stimulation ends. According to him, the researchers also had to take measurements during the rest periods of the test subjects.