There is evidence that fMRI's (functional Magnetic Resonance Imaging) are more effective at detecting 
lies then traditional lie detector tests. Different areas of the brain show greater activity when someone lies then when they tell the truth. It's more work for the brain to lie and fMRI's can detect that activity. However more work still needs to be done. Scans from one individual to another vary greatly so interpretation is still problematic. And there are ethical concerns. Bioethicists warn that "mental privacy" and the Fifth Amendment right to withhold self-incriminating evidence is at risk.
To read more see:
Complex brain imaging is making waves in court
Can MRI Scanner be a lie detector? Experts debate technology
Forensic Psychology and Lie Detection
Posted by Jon Lutz
