Lying studies

Previous studies

From a previous PET study, Abe et al. (2007) differentiated between the process of generating untruthful responses and the social intention to deceive an interrogator. The main effect of generating untruthful responses revealed increased brain activity of the left dorsolateral prefrontal cortex (DLPFC; BA 8) and the right aPFC, whereas the left ventromedial PFC (BA 11) and Amygdala were associated with the process of deceiving the interrogator. 

Furthermore, neuroimaging studies on psychopaths, classified as pathological liars, have demonstrated that they have significantly less gray matter in the PFC (Yang et al. 2005) and that they do not show moral dilemma like healthy subjects (Anderson et al. 1999). 

However, finding brain zones like in the previous studies can only demonstrate correlative behavior and not causal, this was the goal of this experiment, and was possible thnaks to TMS and TDCS.

Interrogation Study

The aim of this study was:

"1) to realize an experimental setup, in which participants should decide themselves, which questions they would answer truthfully and which ones with a lie

2) to investigate the causal contribution of the aPFC in deceptive behavior by modulating the excitability of this brain region through tDCS. Three experiments were conducted to test the specificity of the transcranial stimulation effect."  [1]

The interrogation lasted for 10min and the tDCS started to run 3min before the start, this was to make sure it reached its maximum effects during the interrogation. The first round was done with Cathodal stimulation (inhibition). For the fake stimulation a sham was used that gave the same skin sensation, so that the subject was blind to the intervention effect. 

The Participants stole money from a room and had to then lie about this even in an interrogation. In order to measure 'skillful lying', a ratio called lying quotient (LQ) was developed: 

At the end of each interrogation, the subjects were asked to rate their feelings of guilt that they had experienced while deceiving the interrogator, on a scale from 0 (no feelings of guilt) to 5 (maximum feelings of guilt).

The results based on the LQ showed that subjects with the tDCS stimulation had higher results compared to the sham condition. 

To further prove the results, a control experiment was conducted, where the stimulation polarity was reversed, therefore using the anode. In the anodal case, where the neurons were stimulated to depolarize and therefore activate, there was no significant effect on the reaction time of telling lies. This confirmed the inhibitory influence of the cathode. 

To exclude the option that cathode stimulation on the aPFC influences cognitive demanding tasks in general and not only on deceptive tasks, a third experiment was conducted. Here the same subjects had to solve a demanding task. The results show that cathodal tDCS of the aPFC had no effect on solving the demanding task, suggesting its influence only in deceptive behavior.

Why did the Cathodal tDCS stimulate deception? 

Since the aPFC is crucial for moral reasoning and socio-emotional judgments, reducing its activity may lead to a decrease in moral restraint or emotional conflict, allowing individuals to deceive more easily. Suppressing aPFC activity may reduce guilt and increase antisocial behavior. 

Interestingly, impairments in the aPFC, as seen in psychopaths, are linked to decreased emotional responses and moral reasoning deficits. Studies suggest that dysfunctions in this area may contribute to antisocial behavior, such as lying without guilt. These findings raise important ethical questions about the impact of neurostimulation on moral decision-making and personal responsibility.

Study conclusions

As can be seen from the last experiment, most current experiments focus on enhancing lying ability by inhibiting regions of the brain which correspond to moral decision making and impulse control, but struggle to demonstrate the opposite effect: it is difficult to excite certain areas that correspond to moral reasoning with the effect of making lying more difficult. This is because lying includes intricate neural coordination, moral reasoning and emotion regulation. Most importantly, if a task puts the individual at risk, many factors come at play and more brain regions are activated to try and “save” the subject from saying the truth.