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Crooks Could Fool Brain Scan ‘Lie Detector’

April 19, 2013
Written by: , Filed in: Medical Ethics, Neuroradiology, Pediatric Radiology
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Brain scans can indeed reveal if you remember—or believe you remember—some specific event or person in your life. But the courts that have started to allow them as an evidentiary tool (none of them, so far, in the United States), should beware: people can deliberately fool the scans.

Those are among the conclusions of four research-based presentations Tuesday at the Cognitive Neuroscience Society’s annual meeting in San Francisco.

A news release from the meeting summarizes the four talks. It quotes Anthony Wagner, PhD, who directs the Stanford Memory Laboratory at Stanford University, as saying he got interested in legal applications for brain scans because of a 2008 case in India. A Mumbai judge said EEG evidence indicated a murder suspect had knowledge about the case that only the killer could possess.

The methods used in that case have not been given thorough, peer-reviewed testing. However, Dr. Wagner said:

It appeared that the brain data held considerable sway.

Should it have?

Dr. Wagner and his team recruited volunteers who hung digital cameras around their necks. The cameras automatically photographed daily experiences, generating 45,000 photos per participant over several weeks. The researchers then did functional MRI brain scans of the volunteers as they viewed photos from both their cameras and (as controls) others’ cameras.

“We did quite well with most subjects, with a mean accuracy of 91 percent in discriminating between event sequences that the participant recognized as old and those that the participant perceived as unfamiliar,” Dr. Wagner said.

But in a similar memory test, the researchers stopped halfway through to tell the subjects what the test was trying to do. The researchers then asked the subjects to try to “beat the system.” When presented with an image of an unfamiliar face, the subjects were to think of someone familiar. And when looking at a previously seen face, the subjects were to try to focus on some novel feature of that face.

“In the first half of the test, during which participants were just making memory decisions, we were well above chance in decoding from brain patterns whether they recognized the face or perceived it as novel,” Dr. Wagner said.

“However, in the second half of the test, we were unable to classify whether or not they recognized the face nor whether the face was objectively old or new.”

Clearly, the legal system needs to be very careful—and probably should wait until the technology develops further—before it starts using brain scans as evidence.

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Related seminar: UCSF Neuro and Musculoskeletal Imaging

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