Intense mental work triggers chemical shifts in the brain that temporarily lower the motivation for further effort, according to techno-science.net reporting on 2026-11-08.
A long session of deep thinking can temporarily alter the desire to make an effort, even when a reward makes it worthwhile, leaving people feeling discouraged by simple tasks after a day of solving problems or studying.
To examine this phenomenon, researchers gathered 31 healthy adults. Each volunteer performed a demanding memory exercise for 20 minutes on two separate days, and scientists compared participant reactions before and after the effort.
During one of the sessions, researchers applied a mild electrical stimulation to the head to increase the activity of a region toward the front of the brain, while a simulated stimulation served as comparison during the other session. This forward region is involved in keeping information in memory and manipulating it. By increasing its activity, researchers initially observed improved performance, but this immediate gain carried a trade-off.
Following the exercises, volunteers chose between new memory tasks where easier options paid less money and difficult options paid more. After receiving the genuine stimulation, participants proved less willing to choose tasks requiring high effort, demonstrating that their capacity to succeed and their desire to try again did not necessarily follow the same evolution.
Using a non-invasive imaging technique called magnetic resonance spectroscopy, researchers measured brain molecule concentrations before and after the sessions and observed a higher quantity of glutamate in the stimulated region. Glutamate is a substance nerve cells use to transmit messages that is normally present in the brain and plays a role in its functioning.
While the results connect reinforced brain activity, a measurable chemical change, and a drop in motivation, they do not prove that glutamate alone causes all mental fatigue. Scientists now plan to determine whether this mechanism also occurs in individuals suffering from persistent fatigue, aiming to study whether these chemical changes could help better recognize certain forms of pathological fatigue and subsequently test adapted treatments.
