Brain activity helps detect lies

Brain activity can help detect whether a person is lying or telling the truth. Researchers from the Temple University School of Medicine in Philadelphia used a form of brain imaging called functional magnetic resonance imaging and found that certain regions of the brain lit up when a person lied. In fact, twice as many brain areas were active when study participants practiced deception than when they told the truth. This happens because the brain has to work much harder in lying than in telling the truth. It's too early to judge the practical implications of the findings, but the researchers speculated that functional MRI could offer a more reliable alternative to the traditional polygraph or a lie detector test. Brain activity would presumably be less susceptible to control than the nervous system activities measured by polygraph tests. The polygraph is used in the criminal justice system, but is not infallible. Its lie detection is based on certain changes in a person's sympathetic nervous system activity - increases in heart rate, breathing and perspiration. A shortcoming is that those changes are not unique to lying. General anxiety and anger, for instance, can spur the same physiological responses, and polygraph results appear less accurate when people are telling the truth than when they are lying. Functional MRI measures real-time changes in blood flow in the brain. The results indicate which brain areas are firing during a given activity. In the current study, the researchers had 11 adults undergo both polygraph testing and functional MRI after they had or had not committed a crime. The crime in this case was firing a starter pistol, carrying only blanks, in the research setting. Half of the study participants fired the pistol, while the rest did not. All were told they would be questioned afterward as suspects in the hospital shooting. Five participants were instructed to tell the truth and the other six were told to lie. Along with MRI scans, the subjects underwent a standard polygraph during questioning. Overall, the MRI scans showed that 14 brain areas were significantly activated when study participants were being deceptive, compared with seven that were activated when the subjects were telling the truth. Many of these brain areas are associated with planning, emotion and inhibition, which, in the case of lying, would mean inhibiting the truth. When a person tells the truth, there should be less anxiety and no need for inhibition, so it makes sense that fewer brain regions would be active. The polygraph results were accurate 92 percent of the time when study participants were lying. The test was less adept at spotting the truth - showing 70 percent accuracy. It will be a couple of years, before researchers know whether brain scans can take the place of, or be used along with, polygraph tests.