Low Motivation: What Exactly Happens in Our Brains?

VSEvery day, we complete many tasks that cost us. We gladly accept this effort, knowing that in return we will be rewarded with a salary, or simply the pleasure of completing a project. Sometimes, unfortunately, it becomes difficult to motivate yourself or concentrate. At this point we are talking about real “mental fatigue”. If it mainly happens when we have exhausted all our intellectual resources, it can also be a result of physical fatigue or lack of sleep.

When we are exhausted, we see everything as insurmountable and feel the impossibility of carrying out the slightest activity. What is happening in our brain at this exact moment? Is it the effort required that seems impossible or the reward that suddenly doesn’t seem so motivating? This question is at the center of recent research showing that these two processes can contribute to our demotivation.

In 2010, Julian Lim and his colleagues at the University of Pennsylvania installed participants in a scanner and asked them to respond to a target by pressing a button as soon as it appeared, and this, with constant vigilance, for twenty minutes. During the course of the experiment, they noted not only a gradual increase in the time required to detect the target, but also an increasingly noticeable feeling of mental fatigue.

Their results reveal a cerebral signature of attention and cognitive value in the right hemisphere parieto-frontal network. The activity of this network, which is very important at the beginning of the task, decreases as the feeling of mental fatigue sets in. In addition, brain activity recorded at rest, before the task, in two brain regions, the thalamus and the medial right frontal gyrus, predicted decreased performance during the task. Consequently, there will also be cerebral markers of mental fatigue. But that’s not all: the more we feel tired, the more the reward can lose its value in terms of the required effort.

Limited effect of short breaks

Tanja Müller and her colleagues from Oxford (Great Britain) also installed participants in the scanner in 2021 and asked them to press their hand to receive a reward. On each trial, the subject could choose between five seconds of rest (no force, but negligible reward) and five seconds of more or less intense work associated with a variable reward. Subjects could rate the subjective value of the reward and fatigue. Using this protocol, the authors were able to describe two distinct time scales over which fatigue and reward value decline. This can be observed in the very short term during the task – and, in this case, a short break is beneficial – but the authors also find long-term changes that are not significantly affected by the short break.