NEUROLAW NOVEMBER II – The Opposite of Truth

Imagine a world in which nobody is lying. A world in which no one has ever lied and will never lie. Which problems would emerge? How would life change? There would indeed be fundamental changes. Let us consider an example often used in criminal law classes: A husband whose wife falls in love with another man. Since she will not lie, she tells her husband about it. Out of sorrow and deep hatred, the husband badly wounds his wife. How can we prove this wrongful act? That would be a children’s game, the husband would admit it directly. But that’s not how it works in our real world. There is deceit in our world all the time. From a small child who does not want to admit eating a bit of chocolate after brushing his teeth, manipulated statistics in research, and even blatant fabrications that lead to years of trial proceedings.

To discover an untruth can be tedious and tricky and that is why people have long been concerned about finding out whether someone lies in a simple way. We want to recognize the treachery at the exact moment the person commits it. The basic idea is that a person, whenever a lie is pronounced, gets nervous. In this way we can find physiological changes that can be measured. The vegetative nervous system thus unconsciously leads to several phenomena. These include, for example, changes in blood pressure, respiratory rate and pulse. But at the same time there is also increased electrodermal activity, i.e. the liar begins to sweat. All this happens when our sympathetic nervous system is activated, the component of our vegetative nervous system, which we associate with “Fight or flight”.

One of the most famous polygraphs was constructed by Leonarde Keeler, who was guided by the idea to use his lie detector to replace the violent interrogation methods of the police. Apart from legal successes, however, there were also failures. By self-hypnosis, for example, liars managed not to be recognised as liars by Keeler’s polygraph. The measurement of parameters such as heart rate and skin conductivity did not lead to higher amplitudes in the graphical output of the polygraph. Moreover, it should not be forgotten that lie detectors can not directly discriminate between a lie and the truth; it measures very simple psychophysiological reactions which subsequently need interpretation.

What could we discern if we looked more closely? And indeed, specifically in the “place” where the lies arise? Through the well developed and very accurate methods of the neurosciences, it becomes easier to put the behavior of a person in relation to his brain. For example, we know that activity in the prefrontal cortex is related to the behavior of a person. An analytical method is the functional nuclear magnetic resonance imaging (fMRI). The principle of the fMRI is simple: if a certain brain region is activated, the flow of blood towards it increases. The associated increased oxygen content of this brain region can then be measured. This is due to the fact that oxygenated blood, unlike deoxygenated one, differs in its magnetic properties. This method has often provided evidence there is a connection between behavioral irregularities such as pedophilia and altered brain structures or the cerebral metabolism.[1]

Applying these insights to lying: It could be shown that when telling the truth other brain regions are used than when a person is lying. When lying, the medial posterior cortex is activated. If someone speaks the truth this leads to the activation for example of the right amygdala. But how should we use such results in jurisprudence? Here some practical points should be considered. Up until now, many cortex regions have been identified that are associated with lying. However, it should not be assumed that these areas are not also involved in further brain activities, as this is clearly the case. There is no single area of the human brain that is exclusively attributable to lying. Another question is the extent to which the same areas are still activated in different lies of varying severity in many different individuals. In a recent study, a fairly homogeneous group of participants was examined, but the severity of their lie was low – conclusions are therefore not reliable.

To be able to observe all this and much more, judges and other professionals involved in the decision-making process have to be intensively trained. The limits of neuroimaging have to be acknowledged in order not to lead to false conclusions. The neurosciences cannot abolish the concept of guilt, but they will be able to compel, alter, and expand it in parts. In the experimental context it can be shown whether a statement is false. It seems now to be necessary to discuss whether neuroimaging should become a legitimate tool in the process of evaluating guilt. This is due to the fact that the process of talking to a potentially guilty individual is not always exactly the same. Strict rules, such as the criminal procedure, as they often occur in the natural sciences, cannot exist here. The course of events is often too complex. 

In dubio pro reo & innocent until proven guilty. And precisely for these reasons, defendants may wish that an imaging procedure, even if it is not yet the “hardest” proof of neuroscience, can at least be regarded as an indication of their innocence. If one looks at the opposite case, however, that in which the defendant is proven to be guilty by such a procedure, the value of the neuro-scientific methods seems much lower. According to the current state of research such an indication would probably not qualify as suitable evidence, simultaneously, the defendant would certainly not be interested in it either. Notwithstanding the limitations, it has to be acknowledged that neuroimaging as a useful indicator is already of value today. Concluding with a comparison between neuroscientific imaging procedures and the original polygraphs, neuroimaging seems already more reliable and is set to continue to grow in importance over time. What the future trajectory of this technology will be, time will tell. The fact that lawyers and natural scientists work together is indispensable – and it will be exciting to observe the development of neurolaws in the years to come. 


Also see:

Einsatz bildgebender Verfahren im Strafprozess, (

How predictable are „spontaneuous decisions“ and „hidden intentions“? Comparing classfication results based on previous responses with multivaraite pattern analysis of fMRI BOLD signals (

Das Gehirn auf der Anklagebank, Max Planck Forschung (

Intensivkurs Psychiatrie und Psychotherapie, S. Brunnhuber, Urban&Fischer, 5. Auflage, 2005

Duale Reihe Psychiatrie und Psychotherapie, Hans-Jürgen Möller, Thieme, 3. Auflage, 2005