Why Do We React When We Lie? Take a Cognitive Load Off


Your mind can feel empty if you start lying about something.

I bet you want to know why, when someone asks a question which you have to lie to, you can feel yourself catching your breath, can hear the tumbleweed as it goes through your head and wondering how that 5 second pause could possibly feel so long and awkward?

Maybe you’re not wondering that at all, either way it’s still interesting to learn something new today.

This reaction might be down to a load on your brain, a cognitive load.

What is Cognitive Load?

Today I’m going to briefly expand on something known as cognitive load. It’s not within the scope of this blog to exhaustively explain it and honestly, I don’t think many people need that sort of detail.

What I’m going to do is define it, give it some context and then explain how it relates to the polygraph all based on published research and scholarly articles. Easy peasy right?

Definition of Cognitive Load from Wikipedia.

Definition of Cognitive Load from Wikipedia.

The definition you can see in the picture is from Wikipedia (the fountain of all knowledge). Another definition from the elearning coach states that cognitive load is the ‘total amount of mental activity imposed on the woking memory in any one instant.’

It was first proposed by a gentlemen named John Sweller in the 1980’s for the purpose of helping people to learn complicated theories and concepts more easily.

Could Explain Why Your Brain Hurts

In a nutshell, these complicated learning topics can hurt your brain and reduce the effectiveness of your learning because you are having trouble processing all the novel (new and interesting) stimuli being thrown at you.

A hydrant exploding

Your working memory can only process and handle so much. The internet is one place where it can be flooded.

You and I may call it information overload – at school when the teacher just kept talking about new and interesting (maybe not) concepts in Maths but you started to glaze over because you couldn’t keep up.

That’s a simpler explanation of cognitive load.

To explain what working memory is; it is defined as the mental workspace of the brain that processes and manipulates information.

York University give one example of taking directions; if you don’t have a notepad handy when someone is giving you directions, you try and hold it and remember the information in your head (successfully or not). This is working memory.

Appreciating cognitive load and working memory is all very well and good, but you’re reading a blog about polygraph, so how does cognitive load relate to lie detection?

Cognitive Load & Lie Detection

Starting at the top, there is research to show through fMRI (functional magnetic resonance imaging) to show that when we lie, certain areas of the brain are activated.

If you skip to 4:30 in this video a researcher by the name of Josh Greene at Harvard University explains what is happening in the brain during a lie.

The Brain That Lies

The area seen to be activated the most is the prefrontal cortex. This part of the brain is responsible for all our executive functioning (regulating thoughts and/or actions to achieve goals) including problem solving, planning and attention.

The Truth, The Whole Truth And Nothing But The Truth

What Josh Greene says in the video is that his experiment showed: “this set of brain regions is heavily engaged when people are thinking about whether or not to lie”.

An important point to make is those that lied showed a reaction; however, even when these people were truthful, a reaction was seen. This is thought to be because they showed a conflict i.e. they were considering lying again.

Those who were honest the whole way through and never considered lying showed no activation whatsoever.

Image of the brain

The prefrontal cortex and anterior cingulate cortex are thought to be heavily involved in the decision to lie.

Internal Conflict Area

Interestingly, an area known as the anterior cingulate cortex (ACC) is shown to be activated in some research. The ACC is responsible for what appears to be response conflict i.e. the conflict of telling a truth or a lie.

This brings me round nicely to the fact that research supports the idea that lying appears to be a more psychologically complicated task than truth-telling. We use our brains more when we lie. This suggests that we are naturally wired to tell the truth.

In fact, it has been suggested that we inhibit the truth first in order to tell a lie.

Cognitive Load Experiment

Find a friend or colleague and ask them if they’ll do a little favour for you as part of a small experiment.

  1. Ask them to tell you their mother’s name (insert that persons name as appropriate)
    • “John, do me a favour and tell me your mum’s name please.” “Betty”
  2. Now do ask them the same question, but ask them to lie to you.
    • “Ok, now tell me your mum’s name, but lie to me.” “Urm…Derek!”

Watch their reaction, for the majority of people you will see a pause (a cue to deception), maybe see them flustered etc. etc. you get the point. It’s not a perfect experiment but it goes someway to supporting what I said above.

It's thought that liars are likely to be studying the people they talk to, checking to see if they've been caught.

It’s thought that liars are studying the people they talk to, checking to see if they’ve been caught.

So How Does a Lie Produce a Cognitive Load?

According to a professor named Aldert Vrij there a number of reasons why lying would put a load on the brain and involve the areas we talked about above.

  1. Formulating the lie may be cognitively demanding.
    • A liar needs to invent a story and must monitor that story to make sure it makes sense and then continues to.
  1. Liars are typically less likely than truth tellers to take their credibility for granted.
    • Liars may be more likely to monitor and control their demeanour in order to appear honest.
  1. Liars are unlikely to take their credibility for granted.
    • A continual appraisal of whether the lie is having an affect on the interviewer is also likely behaviour.
  1. Liars may be preoccupied with the task of reminding themselves to role-play and act the part.
  2. As we have seen, liars have to suppress the truth while they are fabricating a lie.
  3. Activation of the lie is more intentional and deliberate, and thus requires mental effort.

Ok great, but how does the polygraph measure all this brain activity?

We strap electrodes to your head and zap you, just kidding.

Some of you may have heard the polygraph as psycho-physiological instrument i.e. when our brain does stuff, our body reacts and we measure it. We don’t measure you brain, we measure your body.

When we are under cognitive load, it induces a sympathetic nervous system arousal. This is part of the autonomic nervous system which we can’t control.

Read these blogs because I explain all the physical components of the polygraph and what they measure and they go into a bit more detail.

In summary though, the sympathetic nervous system causes:

Funnily enough, we have components that measure all of that, hurray!

Please leave me a comment or share this with other people if you enjoy it and think it’s useful. Drop me any questions via the contact form on the ‘Contact Us’ page or any suggestions or things you might want to know about the polygraph.

Leave a Comment

*Required fields Please validate the required fields



Subscribe to our Blog via Email

We will only send you stuff about the polygraph! We will never pass your details on.