We experience mental fatigue when we have been engaged in the same activity, using the same areas of the brain, for an extended period.
The brain uses up more energy than any other organ in the body; approximately 20% of the total consumed glucose energy. Two-thirds of this short-term energy resource is depleted by neuronal communication or nerve cells “firing” or send signals between each other.
So, take for instance you reading this article, the glucose energy is directed to the language, inner ear, and recognition centres of the brain - that’s at least three brain regions energy is distributed to (in reality it’s more) - but you’ve only had one cup of coffee with one teaspoon of sugar that provides your body with a small dose of quick access energy. But you get hooked and end up reading several hours. You have quite literally run out of fuel. As glucose levels drop, levels of adenosine rise. Adenosine is a sleep-promoting, arousal suppressing substance that inhibits the activity of specific neurones, thereby causing us to feel fatigued and sleepy. We now have a problem. Your brain is receiving mixed messages. While running out of energy has triggered a relay action causing you to feel sleepy, you still have caffeine running around your body, demanding energy and also sending messages to suppress adenosine.
So your brain is experiencing a rapid see-saw effect. The remaining third of the short-term glucose energy resource is reserved for brain “housekeeping,” or vital cell-health maintenance keeping us alive. Luckily, adenosine activates the ghrelin hormone making us feel hungry - and we reach for that chocolate croissant!
However, our brain needs periods of rest to function well. For our brain to maintain optimal performance throughout the day, we need a 20-minute shut-down every four hours. Unfortunately, our 8+ hour workday and information-overloaded lifestyle do not allow for regular periods of rest. Thus, we are in a perpetual state of mental fatigue.
Our over-dependancy on our devices further complicates matters, contributing to the Brain Drain Effect. On the one hand, smartphones offer enhanced levels of productivity, attention, and engagement (all very energy-demanding) but on the other, they interrupt our off-screen performance. One interesting study found that the mere presence of our smartphone in our eye-line induces “brain drain” by occupying limited-capacity cognitive resources for purposes of attentional control, thereby impairing decision making.
Why is being ‘overtired’ such a problem when it comes to falling asleep?
As noted above, this is due to mixed messages in the brain and body and habituation of hyper-functionality. To feel like we can fall asleep and to get the best sleep quality, research shows that we need to prepare the mind and body for rest. You cannot expect it to switch off suddenly!
Five tips for helping your brain become less overtired, both through the day and right before bed?
Take periods of active rest every four hours throughout the day. This could be a change of environment or task type, like having a good chat or taking a walk, or meditating. Dr Alex Pang’s book, Rest is filled with the evidence supporting this concept.
Nourish your brain with nutrition that supports optimal brain function. Foods that are high in magnesium, potassium, and fatty acids provide both short-term and long-term energy. So, any leafy greens are vital, so are bananas, and whole grains. Interestingly, Beetroot is high in nitrogen which bonds easily to spare oxygen floating around in your body. This facilitates ATP function, thereby boosting mental performance.
Schedule in device-free time. At least one hour daily, especially before bedtime. And, take a longer digital detox weekly or monthly.
Get in the Green. We have a synergistic relationship with the fauna and flora on this planet - we give them our waste product, CO2 which they need and they give us their waste product, O2 which we need. Research shows that even just looking at a picture of nature triggers memories of the uplifting, energised feeling of being in nature. A 2015 University of Illinois study published in the academic journal of Preventive Medicine discovered that people, sleep better after exposure to natural surroundings.
Practice a pre-sleep ritual. Carve out the last hour in your day to create mental space to process the day. We need time free of sensory distractions to help you wind down your sympathetic nervous system (active) and coaxing the parasympathetic nervous system (rest and digest) to weave its healing magic.