Why you get tired of thinking hard: Glutamate

To find clues, they used magnetic resonance spectroscopy (MRS) to monitor chemical processes in the brain over the course of a working day. MRS is a specialized technique associated with the well-known magnetic resonance imaging, magnetic resonance imaging.

They used this technique to look at two groups of people: one who had to think seriously and one who had to perform relatively easier cognitive tasks.

Only in the group assigned to difficult tasks did they notice signs of fatigue, including dilated pupils. People in this group also showed a shift in their choices toward choices that would yield rewards in the short term and with little effort.

Essentially, they also have higher levels of glutamate at synapses in the prefrontal cortex. Glutamate is the so-called neurotransmitter, a signaling substance that transmits nerve impulses between nerve cells and a gland or muscle cells, and synapses are the contact points where this transmission occurs.

Combined with previous evidence, this supports the theory that glutamate accumulation makes prefrontal cortex activation more difficult. This, in turn, makes cognitive control more difficult after a mentally hard day at work.