Magnetic pulses applied to a specific region of the frontal cortex can influence peoples' willingness to lie spontaneously or tell the truth, according to a new study by researchers from Estonia.

The findings, published recently in the journal Behavioural Brain Research, suggest that manipulations of brain activity could be an effective way of obtaining truthful responses from defendants and criminal suspects, raising more ethical questions about the application of neuroscience technologies in the legal profession.



Dozens of previous studies have investigated differences in the brain mechanisms involved in lying and telling the truth. Typically, these involve scanning participants' brains during simulated lying in mock crime scenarios and looking for differences between the brain activity patterns observed when they are lying and telling the truth, or trying to identify electrical activity that is associated with 'guilty knowledge'.

Inga Karton and Talis Bachmann of the University of Tartu adopted a different and novel approach, by examining the natural propensity to lie spontaneously during situations in which deception has no consequences. They recruited 16 volunteers, and showed them red and blue discs, which were presented randomly on a computer screen. The participants were asked to name the colour of each disc, and that they could do so correctly or incorrectly at their free will.

The researchers used a technique called transcranial magnetic stimulation (TMS) to disrupt the participants' brain activity during the task. TMS is a non-invasive technique in which pulses of electromagnetic radiation are targeted to a specific brain region, inducing weak electrical currents that can either inhibit or enhance activity in that area.

They split the participants into two groups of eight for the experiment. Half of the participants in one group received magnetic pulses to the dorsolateral prefrontal cortex (DLPFC) in the left hemisphere of the brain, while half in the other received them to the DLPFC on the right side. The rest of the participants acted as controls, and TMS was targeted to either the left or the right parietal cortex.

Statistical analysis of the results revealed that magnetic stimulation directed at the left DLPFC slightly increased the participants' tendency to lie about the colour of the discs, whereas stimulation of the right DLPFC slightly reduced it. By contrast, stimulation of the left or right parietal cortex had no effect on the participants' propensity to lie.

"We do not have a good explanation [for this difference], and one can only speculate," says Bachmann. "Lying is a varied, context-dependent behaviour, involving activity in many different functional subsystems. A small, localized spot in brain could not be responsible, and it is very unlikely that we targeted the cortical mechanism involved."

Deception is a complex process, involving a diffuse network that likely contains dozens of brain regions, working in sequence and in parallel. The DLPFC is just one component in this network, and is also involved in numerous other higher order cognitive functions. Earlier research has shown that inhibiting the right DLPFC impairs cognitive control mechanisms, so Bachmann suggests that targeting this region could have increased the automaticity of the participants' responses, making them more likely to tell the truth.

The ability to detect deception accurately is of great interest to the legal profession and security agencies, for obvious reasons. The use of brain scanning data as evidence in courts of law has proven to be highly controversial, not least of all because of doubts about the validity of the data. Some researchers argue that we are now in a position to use functional neuroimaging to detect lies, but the general consensus seems to be that neither the technology nor our understanding of the brain are sophisticated enough.

Bachmann is cautious about how to interpret the new findings, because the sample size of 16 participants is small. He adds that they should be replicated before any firm conclusions can be made about the effects of TMS on spontaneous lying. Even so, the study raises the possibility that TMS could be used to increase the likelihood of getting the truth out of suspects or defendants. It seems likely that some may develop the technique and offer it as a service, as was the case with brain scanning.

"Provided that the method is validated and legal norms are established, it could perhaps be allowed and justified," says Bachmann, "but this should not become a routinely used technique. Basic human rights include cognitive privacy and this would be a clear infringement. If a subject freely agrees, maybe it would make sense, but I foresee heated debates on whether 'knocking truth out of the fellow' can be legalized in principle."

Read Bachmann's full response.

Reference: Karton, I. & Bachmann, T. (2011). Effect of prefrontal transcranial magnetic stimulation on spontaneous truth-telling. Behavioural Brain Research, DOI: 10.1016/j.bbr.2011.07.028