Why Lying Puts Extra Strain on the Brain, and What Researchers Say in a Four-Step Model
Someone is sitting in front of you, speaking fluently. There is no hesitation in their voice and nothing unusual in their expression. Yet a doubt lingers — are they really telling the truth, or are they carefully constructing a lie? Psychologists say there is no simple answer to that question. But trying to understand what happens in a person's brain and emotions while lying may offer some clues to getting closer to the truth.
The first point researchers make clear is that there is no easy formula for detecting lies. Some people become restless while lying, while others try to stay completely normal. So it is not right to call someone a liar just by looking at their eyes, their way of speaking or their body language. Judging from outward behaviour alone can often create a false impression.
Susan Krauss Whitbourne, a psychologist at the University of Massachusetts Amherst in the United States, discussed the mental process behind lying in one of her writings. It emerged there that, compared with telling the truth, lying often requires more mental effort. Lying is therefore not just a matter of words; it also puts extra work on the brain.
When telling the truth, it is usually enough to describe an event or experience one already knows. But the calculation is different when lying. What to say, what to hide, and whether the new statement matches what was said before — all of this has to be managed at the same time. One also cannot say anything that later conflicts with one's own statement. Managing so many calculations at once is what makes lying difficult.
Researchers have seen this extra mental strain as an important feature of lying. While lying, a person has to exercise extra control over their own statement. In psychology, a related process is called 'response inhibition' — that is, controlling what one immediately wants to say and instead giving a planned answer. That control, holding back the truth and delivering a constructed answer, is what makes the brain work harder.
But not everyone lies in the same way. Some prepare a story in advance, while others create answers according to the situation. As a result, the mental strain of lying can also differ from person to person and situation to situation. The strain in a pre-planned lie is one kind, and the strain in a lie created suddenly in the face of a question is another — that difference has also received importance in the research.
It is not only the brain's extra effort that plays a role while lying; emotions also matter. Someone may suffer from guilt, someone may be anxious about being caught, and someone may even feel temporary satisfaction from lying. This mixed emotional reaction makes the experience of lying different for different people.
In particular, nervousness or mental tension can increase when lying about an event from one's own past. However, experienced liars can learn to control their emotions. So one cannot conclude that someone is lying just because they look anxious. People can also feel fear, pressure or discomfort while telling the truth — researchers have repeatedly reminded readers of that caution.
In 2026, researchers Tabea Wachtershauser and Christina Suchotski of the University of Marburg in Germany discussed a four-step model to explain the mental process of lying. It is called 'Activation-Decision-Construction-Action'. The model provides a framework for understanding the whole process of lying step by step.
In simple terms, the process of lying can proceed like this — first, the truth becomes active in the mind; the person knows what actually happened. Next, they decide whether to reveal the truth or conceal it. Then they arrange what to say instead of the truth, how to say it and how to make the statement believable. Finally, they present the constructed statement to others. This whole process requires remembering information, building answers and maintaining consistency with one's own statement, so lying often demands more mental effort than telling the truth.
The researchers compared participants' experiences of lying and telling the truth in two experiments. Participants were placed in a fictional theft scenario. In one experiment a USB drive was used, and in the other a situation involving the theft of one thousand euros was created. They were then asked questions designed to reveal differences in reaction speed and emotion between lying and telling the truth. The results showed that participants took more time to lie than to tell the truth. At the same time, they reported more fear, nervousness and mental discomfort while lying.
However, this research also has limitations. Participants in the experiments knew that the researchers were aware of the whole event. Real-life situations can be different from that. So laboratory results cannot be used to judge every lie in everyday life. Still, the research makes one thing clear — lying is extra work for the brain, and traces of that extra work can appear in timing and emotion, although they can never on their own prove someone to be a liar.
