Brain Fingerprinting - Background and Terminology

Background and Terminology

"Brain fingerprinting" is a computer-based test that is designed to discover, document, and provide evidence of guilty knowledge regarding crimes, and to identify individuals with a specific training or expertise such as members of dormant terrorist cells or bomb makers. It has also been used to evaluate brain functioning as a means of early detection of Alzheimer's and other cognitively degenerative diseases, and to evaluate the effectiveness of advertising by measuring brain responses.

The technique is described in Dr. Farwell's paper "Using Brain MERMER Testing to Detect Concealed Knowledge Despite Efforts to Conceal", published in the Journal of Forensic Sciences in 2001 by Dr. Farwell and FBI Supervisory Special Agent Sharon Smith of the FBI (Farwell & Smith 2001).

The paper describes a test of brain fingerprinting, a technology based on EEG that is purported to be able to detect the existence of prior knowledge or memory in the brain. The P300 occurs when the tested subject is presented with a rarely occurring stimulus that is significant in context (for example, in the context of a crime) (Gaillard & Ritter 1983, Farwell & Donchin 1991). When an irrelevant stimulus is presented, a P300 is not expected to occur (Picton 1988, Farwell & Donchin 1991, Farwell & Smith 2001). The P300 is widely known in the scientific community, and is also known as an oddball-evoked P300 (see Harrington v. State 2001 and P300).

While researching the P300, Dr. Farwell created a more detailed test that not only includes the P300, but also observes the stimulus response up to 1400 ms after the stimulus. He calls this brain response a MERMER, memory and encoding related multifaceted electroencephalographic response. The P300, an electrically positive component, is maximal at the midline parietal area of the head and has a peak latency of approximately 300 to 800 milliseconds. The MERMER includes the P300 and also includes an electrically negative component, with an onset latency of approximately 800-1200ms (Farwell 1994, Farwell & Smith 2001). According to Dr. Farwell, the MERMER includes additional features involving changes in the frequency of the EEG signal, but for the purposes of signal detection and practical application the MERMER is sufficiently characterized by the P300 and the following negative component in the brain response (Farwell 1994, Farwell & Smith 2001, Farwell et al. 2006).