Brain MRI stands up to polygraph test

January 30, 2006

Traditional polygraph tests to determine whether someone is lying may take a back seat to fMRI, according to a study in the February issue of Radiology. Researchers from Temple University Hospital used fMRI to show how specific areas of the brain light up when a person tells a lie.

Traditional polygraph tests to determine whether someone is lying may take a back seat to fMRI, according to a study in the February issue of Radiology. Researchers from Temple University Hospital used fMRI to show how specific areas of the brain light up when a person tells a lie.

"We have detected areas of the brain activated by deception and truth telling by using a method that is verifiable against the current gold standard method of lie detection - the conventional polygraph," said lead author Feroze B. Mohamed, Ph.D., an associate professor of radiology at Temple.

Standard polygraph tests have failed to produce consistently reliable results, largely because they rely on outward manifestations of certain emotions that people feel when lying. These include increased perspiration, changing body positions, and subtle facial expressions. While natural, they can be suppressed by a large enough number of people that the accuracy and consistency of the polygraph results are compromised.

"Since brain activation is arguably less susceptible to being controlled by an individual, our research will hopefully eliminate the shortcomings of the conventional polygraph test and produce a new method of objective lie detection that can be used reliably in a courtroom or other setting," Mohamed said.

Researchers recruited 11 subjects for the study. They staged a mock shooting, in which blank bullets were fired in a testing room. Five volunteers were asked to tell the truth when asked a series of questions about their involvement, and six were asked to deliberately lie.

Each volunteer was examined with fMRI to observe brain activation while they answered questions either truthfully or deceptively. They also underwent a conventional polygraph test. The same questions were asked in both exams, and results were compared among the groups.

"With fMRI, there were, consistently, unique areas of the brain - and more of them - that were activated during the deceptive process than during truth telling," Mohamed said.

In producing a deceptive response, a person must inhibit or conceal the truth, which activates parts of the brain that are not required for truth telling. Thus, telling the truth activates fewer areas of the brain.

Fourteen areas of the brain were active during the deceptive process. In contrast, only seven areas lit up when subjects answered truthfully. By studying the images, investigators were able to develop a better picture of the deception process in the brain. The increased activity in the frontal lobe, especially, indicated how the brain works to inhibit the truth and construct a lie.

Polygraph test results correlated well with actual events when subjects were asked to lie (92% accuracy). The results were less conclusive, however, when subjects were asked to tell the truth (70% accuracy).

The largest implications for a credible method of lie detection are in the field of crime investigation and prevention and in the judicial determination of the guilt or innocence of accused individuals. Since the polygraph has not been embraced as fully credible, the authors hope to provide a more accurate means of determining whether someone is telling the truth.

"A more consistent and verifiable method of lie detection could lead to changes in this particular realm of the legal system down the road," Mohamed said.

For more information from the Diagnostic Imaging archives:

Functional MRI sniffs out liars and cheats

Strategic goals take shape in functional brain MR imaging

Functional imaging leads hunt for 'buy' trigger

Functional MRI speeds psych drug development