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Brain scan is more effective than polygraph test in detecting lies

sex-and-relationships Updated: Nov 05, 2016 12:58 IST
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Scanning people’s brains with fMRI is significantly more effective at spotting lies than a traditional polygraph test, claim researchers. (Shutterstock)

When it comes to lying, our brains are much more likely to give us away than sweaty palms or spikes in heart rate, a new study has found.

Researchers at University of Pennsylvania in the US found that scanning people’s brains with fMRI, or functional magnetic resonance imaging, was significantly more effective at spotting lies than a traditional polygraph test.

The study was the first to compare the fMRI scan and polygraph in the same individuals in a blinded and prospective fashion.

The approach adds scientific data to the long-standing debate about this technology and builds the case for more studies investigating its potential real-life applications, such as evidence in the criminal legal proceedings.

Researchers found that neuroscience experts without prior experience in lie detection, using fMRI data, were 24 per cent more likely to detect deception than professional polygraph examiners reviewing polygraph recordings.

In both fMRI and polygraph, participants took a standardised “concealed information” test.

Polygraph, the only physiological lie detector in worldwide use since it was introduced in its present form more than 50 years ago, monitors individual’s electrical skin conductivity, heart rate and respiration during a series of questions.

“Polygraph measures reflect complex activity of the peripheral nervous system that is reduced to only a few parameters, while fMRI is looking at thousands of brain clusters with higher resolution in both space and time,” said lead author Daniel D Langleben, professor at Penn.

“While neither type of activity is unique to lying, we expected brain activity to be a more specific marker, and this is what I believe we found,” said Langleben.

To compare the two technologies, 28 participants were given the so-called “Concealed Information Test” (CIT).

CIT is designed to determine whether a person has specific knowledge by asking carefully constructed questions, some of which have known answers, and looking for responses that are accompanied by spikes in physiological activity.

Sometimes referred to as the Guilty Knowledge Test, CIT has been developed and used by polygraph examiners to demonstrate the effectiveness of their methods to subjects prior to the actual polygraph examination.

In the study, a polygraph examiner asked participants to secretly write down a number between three and eight.

Next, each person was administered the CIT while either hooked to a polygraph or lying inside an MRI scanner. Each of the participants had both tests, in a different order, a few hours apart.

During both sessions, they were instructed to answer “no” to questions about all the numbers, making one of the six answers a lie.

The results were then evaluated by three polygraph and three neuroimaging experts separately and then compared to determine which technology was better at detecting the fib.

The study was published in the Journal of Clinical Psychiatry.

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