When somebody lies, they activate three key areas of the brain: the prefrontal cortex (responsible for thinking and planning), parietal lobes (involved in self-monitoring based on the environment) and the anterior cingulate cortex (supports attention and working memory). These three areas are extremely demanding and require more conscious effort than usual. Some studies suggest that this extra cognitive load produces subtle behavioural results.
1. Slower speech and pauses
Many people believe that liars often speak fast and overexplain, but several studies report the opposite – pauses and delays in speech. The longer it takes to respond, the more likely it could be perceived as a lie. This happens because the prefrontal cortex becomes highly active when lying, and this part of the brain works harder than usual. Because of the increased brain activity, it takes longer to get the new story straight and work out the details, resulting in slower speech and more pauses.
2. Stillness and frozen body
Despite often expecting liars to fidget and appear nervous, in reality, they may become more still and composed. Because of the mental energy taken up, the brain is extremely busy managing the lie, recalling details and making their story consistent. The body may respond by reducing movement to maintain focus and conserve energy. For some, this can result in more deliberate and controlled hand gestures and movements.
3. Talking too little
The best liars speak quickly to conceal their deceit; however, not everyone is a good liar. Shorter responses and fewer details are common due to the energy it takes to come up with a lie on the spot. Additionally, liars don’t want to be found out, providing as few details as possible to reduce the risk of slipping up. If someone usually speaks more and this behaviour seems out of character, this can be a strong indicator.
4. Sweating and dry mouth
Alongside the verbal cues, physical signs of stress are a big indicator of whether or not somebody’s lying. It’s thought that the fight or flight response may come into action when lying, especially if there is any feeling of guilt. This trigger manifests in a variety of physical signs, including sweating, which is stimulated by adrenaline and similar hormones, and dry mouth, which is a result of the body redirecting blood flow away from saliva production.
5. Unnatural eye contact
A 2016 study found that gaze aversion was the behaviour most associated with deception, but this isn’t necessarily true. There is no reliable indicator that a lack of eye contact means someone is lying. However, a change in normal eye behaviour should be taken into account. Because lying takes effort, people often try to control their behaviour and often overcompensate with eye contact. This can be a visible effect of the brain’s effort to self-monitor whilst lying.
