26 Oct 2023

Fatigue – are you feeling it?

Fatigue – I wonder if this is one of the most used words to describe how we have been feeling, and still feel, across 2022 and 2023.  There seems to be very few people that are not feeling fatigued in some form, and I am curious to understand what is going on!


I think there are a number of elements to what is causing our ‘fatigue’ and one of these elements is defined in the following article by Andy Habermacher (August 2022), and will make sense, whether we do, or do not, fully understand the neurobiology!


We all know that feeling of having engaged in hard cognitive, thinking, tasks, and feeling tired. If it goes on long enough, we may feel mentally fatigued, drained, or even exhausted.

But why?

We tend to know that physical activity uses a lot of energy and so will tire you out, but mental activity less so. So why does this happen? And researchers, though they know the feelings themselves as much as the average person in the street, haven’t been able to give a clear explanation.

This latest piece of research by Wiehler et al. has managed to find out the precise cause of this. To do this the researchers measured participants over a day and used brain scanning to elucidate changes in brain functioning. This is a pretty cool research protocol because it represents real-life functioning of real-life people. There were two groups: those with cognitively demanding jobs and those with less cognitively demanding jobs. At the end of the day, they were given various cognitive tasks in a brain scanner.



What did they find?



They found that a part of the brain called the prefrontal cortex exhibited signs of fatigue. The prefrontal cortex is considered our “executive centre” or thinking part of the brain that is involved in control, intentional thought, calculations, and decision-making. This was in comparison to other regions of the brain.

This fatigue led to altered processing and altered decision making with a preference for easier decisions or pathways. So, when tired, you go for the easy solution or draw on a habit. We already knew that, but more than that, they were able to identify the mechanisms. The results of this showed that the fatigue led to a build-up of waste products that can become potentially toxic in the region. The brain uses chemicals to generate the electrical impulses and if these can’t be cleared away, they lead to build up between the neurons. This alters processing but also increases the cost of processing. They specifically were able to measure increased glutamate in the prefrontal cortices of those in the cognitive effort group. Glutamate is common chemical in the brain used for processing signals.

So, this shows that fatigue is not just “psychological” but is also based on biological mechanisms with the build-up of substances which impede and alter processing. This feeling of fatigue is therefore your brain trying to rest, to stop this build up, and allow cleaning out of toxic substances. Fatigue is after all a sign of needing a rest – but the downside is that this will also lead your brain to avoid thinking as much and take easy options – which could be worse decisions, or alternatively, succumbing to an unhealthy snack.

It will be hard to avoid this totally, but this shows why the good old advice of having regular breaks really is very, very important. And why you should have breaks before you get tired. It also shows that you shouldn’t make important decisions at the end of the day!


Andy Habermacher is author of Leading Brains Review, Neuroleadership, and multiple other books. He has been intensively involved in writing and research into neuroleadership and is considered one of Europe’s leading experts. He is also a well-known public speaker, speaking on the brain and human behaviour. https://leading-brains.com/


Reference: Antonius Wiehler, Francesca Branzoli, Isaac Adanyeguh, Fanny Mochel, Mathias Pessiglione “A neuro-metabolic account of why daylong cognitive work alters the control of economic decisions”Current Biology, 2022


Jean Schoultz | People & Culture Specialist