While a standard polygraph test can be beaten by training, a new method of lie detection involves the use of an MRI. Known as brain fingerprinting, this method detects responses to certain stimuli within the brain, something much more difficult to mask.
The subject being tested wears a special headband and undergoes a base-line testing similar to a standard polygraph, being shown images or presented with other stimuli which are meant to be neutral and some which are meant to elicit a particular response. The test is looking for an electrical signal known as P300 which is emitted from an individual's brain approximately
300 ms after it is confronted with a stimulus of special significance. The key to brain fingerprinting is to look for P300 as
response to stimuli related to the crime in question - for example a murder weapon or a victim's face. More information can be found at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3311838/
