We all know the feeling of being tired.  Basically, it results in a lack of strength which happens after we have worked hard either physically, intellectually or emotionally.  We can also feel tired as a result of boredom, unhappiness, disappointment or annoyance.

The effect of being tired on our behaviour is also apparent and we find it harder to control ourselves when fatigued.  Children especially tend to behave ‘badly’ when they are tired, as we know. But why is this?

David Bueno I Torrens explains this to The Conversation by looking at how the brain works.

Behavioral control is handled specifically by an area called the prefrontal cortex, located just behind the forehead. This area is responsible for all executive functions, like planning, making decisions, reasoning and managing our emotional state.  In addition, it is responsible for our working memory and the brain’s ability to adapt our behaviour and thinking to changing situations or concepts.   

These (and other) functions take a great deal of the energy available to the brain.  When we are tired, the prefrontal cortex is depleted of the fuel needed to think, plan, decide, manage emotions and store and handle information.

In other words, we find it harder to think, plan, decide, manage emotions and store and handle information because the prefrontal cortex has less fuel to function. This also makes our thoughts less flexible and more rigid. As a consequence, we lose the ability to control our behaviour.

The same is true of tired children.  Without sufficient brain energy to work efficiently, they might do things that they usually wouldn’t do, say things they know are hurtful, and generally ‘misbehave.’

Boredom has a similar effect to tiredness

Interestingly, when we are bored, disappointed or angry, something similar happens; although the reason is slightly different.

When we are demotivated, the brain also receives less energy, meaning that the prefrontal cortex cannot function at full capacity. Or, to put it the other way round, motivation increases the blood flow to the brain and, with it, the available energy, which in general improves the functionality of executive functions.

That is why, when we are motivated we usually think, plan and decide better, and can manage our emotions much better.  

Provided by The Conversation