Imagine a suspected criminal facing a computer screen while strapped to an electrode-studded headband. Details known only by the police and the perpetrator—crime-scene photos or phrases such as butcher knife—flash on the screen. If a suspect recognizes the stimuli, the brain involuntarily emits an incriminating brain wave.
The scenario's not as far-fetched as it sounds. Indeed, so-called brain fingerprinting has been proved to work in nearly 200 tests conducted—many by the FBI, CIA, and U.S. Navy.
While lie-detector tests measure sweating and heartbeat changes, brain fingerprinting records an electric signal called a MERMER emitted by the brain before the body physically reacts. "It does not test absolute truth or the contents of memory," says Lawrence Farwell, the neuroscientist who founded Brain Fingerprinting Laboratories in Fairfield, Iowa. Farwell notes the test is voluntary and can only be requested by a suspect if investigators have plenty of specific evidence related to the crime.
An Iowa judge ruled brain fingerprinting admissible in court in 2001 after it was tested and peer-reviewed in the Journal of Forensic Sciences. A few years ago, the Iowa Supreme Court exonerated a convicted murderer through brain fingerprinting. The man had spent 25 years in prison.