Details of any crime are always imprinted on the brain of the criminal that can be retrieved and recorded on an Electro-encephalograph (EEG). This is the philosophy behind a novel test to catch the actual culprit.
When the brain recognizes something, the memory centers are stimulated. The neurons fire synchronously, eliciting characteristic changes in brain activity. It is these changes, which can be measured using electrodes, which investigators look for when trying to determine whether someone recognizes a particular piece of information.
The conventional polygraphs, or lie detector tests, are based on emotional responses to stress such as increased heartbeat and blood pressure, and excessive sweating; these responses can be faked.
But regardless of the verbal response of the suspect, his brain will always tell the truth. Discovering this answer from the involuntary brain activity is the task of a new investigating tool, called brain fingerprinting (BF). By tapping into the specific information stored in a person’s memory, BF provides a scientific solution to the problem of identifying criminals and trained terrorists. This test of guilt or innocence has been ruled admissible inUScourt, implying that this new branch of forensic science has the potential to revolutionize the whole criminal investigation and justice system.
Event Related Potential (ERP) and P300 Response
Buried in the EEG are also signals that reveal information about brain processes. These signals are detected by timing changes in the EEG after events such as listening to a sound or viewing a picture. The resulting activity is called an event related potential (ERP), which clearly stands above the background brain activity. Generally, the signals occurring after 250 milliseconds are thought to reflect higher level cognitive processes such as memory or language.
Stating more clearly, when a subject recognizes an information out of a series of irrelevant information, a signal is emitted, typically within 300–1000 millisecond after the stimulus, called a P300 response. For example, if a subject is exposed to a series of random names and occasionally his own name, a P300 response is evoked.
The utility of the P300 in detection of deception was recognized as early as 1988, when it was shown that it could be used to identify college students who were lying to lie after stealing something. However, the P300 has only about 878 percent success rate in revealing the presence of relevant information.
Go for MERMER, Not Just P300
Dr Lawrence Farwell improvised on the P300 test; he recognized that the P300 is only a subcomponent of a more complicated response called a MERMER, which is elicited when a person recognizes and processes a stimulus that is particularly noteworthy to him/her. The MERMER (Memory and Encoding Related Multifaceted Electroencephalographic Response) includes the P300 and another longer latency, electrically negative subcomponent with a latency of up to two seconds post-stimulus. In other words, a positive wave followed by a negative one. Tests using the MERMER produced no false negatives or positives and no indeterminates.
When details of a crime are known to the suspect, a MERMER will be detected. A MERMER will not occur in an innocent subject.
How Brain Fingerprinting is Conducted
Multiple-choice test for the brain
The test involves three kinds of information to determine whether a subject has specific crime-related information in his brain:
- Targets: information the subject definitely knows; this can be ensured by telling the subject before the test starts.
- Irrelevants: information that subject definitely does not know; this can be ensured by simply making up the information.
- Probes: information relevant to the crime or situation, which the subject may or may not know. It can be anything from a phone number to an al-Qaeda code word.
The response of the brain to information is measured using a headband with electrodes. Target information elicits a ‘yes’ response or a MERMER. This is used as a control. Irrelevant information will not elicit a MERMER. A MERMER in response to probe stimulus indicates recognition or the presence of certain information.