Application in deception

Study from Helsinki on left and right DLPFC

Although many regions are also active when deception isn’t taking place, an increasing number of experiments seem to show that the dorsolateral prefrontal cortex (DLPFC) is associated with lying. Furthermore, there seems to be a distinction between right and left DLPFC:

• the right side of the DLPFC: seems to be more correlated in cognitive control, avoidance and behavioral inhibition. 

• the left DLPFC: is involved in reality monitoring, approach motivation, strategic behavior, naming and execution. 

Indications of correlation

Prior to this study, small experiments were conducted, for example:  

“Where subjects had freedom to name presented stimulus-objects (red and blue colored circles) either veridically or nonveridically the amount of truthful answers can be manipulated by inhibitory off-line 1-Hz repetitive transcranial magnetic stimulation targeted at DLPFC: inhibition of the left DLPFC with rTMS increased the relative rate of lying, but inhibition of the right DLPFC decreased it. In the second study, the subjects were allowed to report the name of the shape (circle or square) of the object they actually saw or report the name of the object they did not actually see, therefore producing a non-truthful response. When trains of 10-Hz pulses were delivered to the right DLPFC, propensity to lie increased while similar left-hemisphere DLPFC stimulation did not change the rate of untruthful responses.”

The study

A second experiment followed, in which the subjects had to name the circle presented either as blue or red. To stimulate the participants in wanting to lie, they were told that they would be paid more the more red circles they named. 

However, to have a control and also sometimes have the truth said, there were randomised checks. If during a check the lie was detected (the patient said red and it was blue), the subject would lose points.

All subjects received all stimulation conditions (left and right 1-Hz and sham; left and right 10-Hz and sham) and noise was always added so the subjects couldn’t detect when the TMS was active and when it was not. 

The conclusion of this study showed that excitation had different effects when stimulation was applied to the right and left hemisphere:

• Excitation of the left DLPFC with rTMS: tended to decrease lying 

• Excitation of the right DLPFC: showed that the lying rate slightly increased

Unlike previous experiments, inhibition of the DLPFC did not produce the expected opposite effects.

This is probably due to differences in behavioural tasks. In the second experiment, the task performance lasted longer and therefore the rTMS application was not enough to induce a significant change in behavior. In addition, the second experiment included the context of risk-taking game, which is much more complex and involves more networks, compared to lying with no consequence. 

TMS compared to TES in lying studies 

In this Study, it was actually possible to inhibit an area and find a decrease in the mean lying rate. In the TES case, this was probably not possible as TES applies weak electrical currents to the scalp to modulate neuronal excitability rather than directly inhibiting activity. This means, that it's less precise compared to TMS and generally shifts neurons closer to or farther from their firing threshold, without strongly suppressing or activating specific areas.

Lying involves complex networks, making the strong, focal inhibition provided by TMS is more effective than TES for observing changes in behavior. TES might influence excitability but isn’t powerful enough to inhibit regions significantly, hence its limitations in such studies.