MadSci Network: Neuroscience
Query:

Re: Can we use PET scan or MRI scan for lie detection?

Date: Mon Jun 11 10:46:08 2001
Posted By: Eric Tardif, Post-doc/Fellow, Institut de Physiologie, Université de Lausanne
Area of science: Neuroscience
ID: 991246387.Ns
Message:

Dear Senthil,

What is commonly called « lie detector » is actually a polygraph that 
essentially measures four parameters : heart rate, blood pressure, 
respiration, and sweating (see the image at the bottom). The variation of 
these parameters may be associated with some emotions but the question is 
highly controversial. To my opinion, what should be clear is that the 
polygraph measures the parameters mentioned above but not in any way 
whether a person is telling the truth or not. Moreover, the output from a 
polygraph may fail to detect real emotions (ex. fear) behind lying. 
Indeed, a 1983 report by the Office of Technology Assessment concluded 
that polygraphs are not an effective scientific method to check for 
security breaches. I also think that having “false positive” is very 
dangerous: a person may tell the truth while being highly stressed by the 
situation. According to Alan P. Zelicoff (physicist at the Center for 
National Security and Arms Control at Sandia National Laboratories in 
Albuquerque, New Mexico): there are  “tremendous cynicism and doubt about 
the utility of the test in both management and technical staff.”

To answer your question more precisely, there are no study that have used 
PET or fMRI as a “lie detector”. On the other hand, some people think that 
it would yield better results than the polygraph because there are growing 
evidence that certain parts of the brain are involved with emotions 
(discussed briefly in Holden, 2001). On the other hand, one must remember 
that emotions does not necessarily mean truth or lie although it may be 
indicative in some cases.

Thanks for the interesting question!
Eric

See also:

Holden C. (2001) 
Polygraph screening. Panel seeks truth in lie detector debate. 
Science 291(5506):967.

Lykken DT. (1991) 
Why (some) Americans believe in the lie detector while others believe in 
the guilty knowledge test. 
Integr Physiol Behav Sci 26(3):214-22.

















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