MYTH: IS IT POSSIBLE TO BEAT A LIE DETECTOR TEST?

Finding: PLAUSIBLE

Explanation: Criminal investigators claim that polygraph machines are 80 to 99 percent accurate at fingering fibs, but conflicting research contends that their track record is flimsy at best. According to a study from the National Research Council, a nervous or intimidated person telling the truth could easily give off physical stress signals associated with lying, for instance. To set the record straight, MythBusters Kari Byron, Grant Imahara and Tory Belleci attempted to trip up two types of lie detector tests — a traditional polygraph test that measures physiological signs of stress and functional MRI (fMRI) scans that track blood flow in the brain.

For the polygraph experiment, Tory pinpricked himself and bit his tongue when answering questions truthfully in an effort to induce stress responses, including increased heart rate, blood pressure and sweating. Theoretically, keeping his physical reactions amped up like this should counterbalance any stress signals registered when he lied. But Tory's pain was in vain when the machine still spotted his lies.

Grant, on the other hand, tried to use his mind to out-fox the polygraph: He conjured up happy thoughts while lying and stressful ones while telling the truth to muddy the results. However, he couldn't think away his sweating skin, which is what ultimately betrayed him. The team wasn't able to bust the polygraph, but that isn't the only lie detection test on the block.

To take on the fMRI, which can supposedly detect differences in brain blood flow when lying, all three MythBusters turned to mind games. Tory and Kari mimicked Grant's polygraph plan of alternating between happy and sad thoughts — and failed the test. Grant focused on his fears in hopes of stimulating blood circulation in multiple brain regions. Apparently, Grant is pretty good at scaring himself: He was so distraught by the time he took the test, the brain scans didn't show any signs of his subterfuge.

Caught by the polygraph but having beaten the fMRI only once, the MythBusters declared it plausible to beat a lie detection test. Just because the team demonstrated lackluster lying skills doesn't mean someone else couldn't slip under the radar — though the best policy is probably to stay out of trouble in the first place.

As seen in "MythBusters: Confederate Steam Gun".

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