American Journal of Law & Medicine

Emerging neurotechnologies for lie detection and the Fifth Amendment.(Brain Imaging and the Law)


The development of a successful lie detector has been a dream of governments and law enforcement since ancient times. A Hindu Veda written around 900 B.C.E. suggests a strategy for detecting lying behavior in suspects:

   A person who gives poison may be recognized. He does not answer 
   questions, or they are evasive answers; he speaks nonsense, rubs 
   the great toe along the ground, and shivers; his face is 
   discolored; he rubs the roots of the hair with his fingers; and he 
   tries by every means to leave the house.... (1) 

Six hundred years later, the Greeks were attempting to detect lies by feeling the suspect's pulse. (2) What is interesting about both the early Hindu and Greek examples is that the methods employed were empirical; the interrogators were looking for physiological changes in the body that corresponded to the mental state in question. In contrast, the "Ordeal" strategy that dominated Christian Europe (and other places, including India) for centuries was based on a belief that God would intervene to reveal who was guilty and who was innocent. (3) Interrogators determined whether subjects were lying by seeking a variety of supernatural indicators. Psychological and physiological factors were deemed irrelevant (except, perhaps, the psychology of wrenching confessions from those fearful of red-hot irons, boiling water, or drowning). (4) Interrogators determined whether subjects were lying by seeking supernatural intervention.

Lie detection strategies have advanced little over the methods used by the ancient Greeks. Asking calculated questions and "feeling the subject's pulse" is still a dominant strategy. (5) Of course, modern polygraphy includes measures of respiration, perspiration, and blood pressure, and can determine changes in heart rate much more accurately than placing a finger on the suspect's wrist. Still, using physiological changes in the peripheral nervous system (PNS) to measure deception has proven to be unreliable. (6) Even strategies that do not use physiological measurements, like Paul Ekman's use of microfacial expressions, still involve analyzing an indirect measure of deception expressed by the PNS. (7)

Recently, however, neuroscience has, for the first time in history, allowed researchers to bypass the PNS and gather data directly from the brain. (8) Several new technologies use measurements of blood flow or electrical impulses in the brain to identify distinct indicators of deceptive communication. These technologies are referred to as "Neurotechnological Lie Detection" (hereinafter "NTLD"). They endeavor to measure lying more directly by measuring brain activity rather than second-order indicators like pulse or respiration.


There are two main categories of NTLD. The first involves determining blood flow patterns in the brain. By studying blood flow patterns during deception and comparing them to blood flow patterns during non-deception in similar situations, researchers can learn which regions of the brain are activated when people are lying. (9) Functional Magnetic Resonance Imaging (fMRI) is currently the most commonly used method for measuring blood flow in the brain. (10) While such brain imaging technologies are the most robust means of determining blood flow during deception, two other techniques have also been shown to have utility: (1) functional near-infrared light technology (fNIR), (11) which reflects infrared light off the frontal cortex transcranially, and (2) thermographic technology, which detects heat emanating from the skin of the face. (12) Researchers have conducted experiments with these techniques using playing cards and other constructed scenarios that elicit lying behavior. (13)

Newer imaging technologies may be even more reliable as lie detectors. Traditionally, for example, neuroimaging has correlated external situations to responses in specific areas of the brain. (14) The goal was to determine which discrete areas of the brain were employed in specific kinds of tasks, behaviors, or cognitive and affective states. Once it was known which areas of the brain were activated, researchers could use activation of those parts to determine what target behavior the subject was engaged in. (15) Now, however, the science has advanced to the study of general patterns of brain activation distributed over many regions of the brain. (16) Researchers attempt to use these patterns to predict generally what kinds of actual cognitive activities the person is engaged in. If perfected, this strategy could enable much more accurate predictions of cognitive and affective states.

Brain imaging requires large machinery and sophisticated technicians, (17) and although fNIR and thermographic equipment is much more mobile, (18) these methods are almost certainly less accurate at present. (19) Even the most accurate lie detection techniques are, at this point, unproven. Nevertheless, two companies have already been incorporated with the intention of offering these services to the public. (20)

The second category of NTLD covers techniques that use event related potentials (ERPs) through electroencephalogram (EEG) to identify patterns of recognition. (21) Proponents claim that these techniques can be used to confirm or refute a subject's claims, or to indicate the presence of certain kinds of concealed information. (22) With EEG, the researcher uses electrodes placed on the subject's scalp to detect and measure patterns of electrical activity emanating from the brain. (23)

For the purposes of this Article, it is instructive to look at one patented form of this technology: "brain fingerprinting." Developed by Dr. Lawrence Farwell, founder and chief scientist of Brain Fingerprinting Laboratories, brain fingerprinting attempts to discern whether a person has knowledge of a particular event or an image (such as a crime scene under investigation) stored in his brain. (24) The subject is seated in front of a computer screen and wears a headband with sensors that measure EEG responses at several locations on the scalp. (25) The subject is told that he will be presented with a series of words or images. (26) Before the testing begins, he is given a list of target stimuli, to which he is told to pay particular attention. (27) He is instructed to hit one button when a target stimulus appears, and another button when any other stimulus appears. (28) The subject is then presented with a variety of stimuli for a fraction of a second each. (29) In addition to these "targets," two other types of stimuli are presented: "probes" and "irrelevants." (30) The "probes" are stimuli that relate to the topic at issue, such as a photograph of a crime scene. The "irrelevants" bear no relation at all to the topic at issue. (31) As the subject views these images, his EEG responses are recorded. (32)

Practitioners believe that each bit of information stored in the brain is stored by specific neurons and that if the brain recognizes a salient piece of information, specific neurons fire in response. (33) The firing of neurons generates an ERP component called the P300. (34) This occurs 300 milliseconds after the subject is exposed to a stimulus. (35) Because the subject has been told to pay particular attention to the target, this stimulus will be salient to the subject and will create a baseline P300 response or "Memory and Encoding Related Multifaceted Electroencephalographic Response" ("MERMER"). (36) A MERMER response indicates that information regarding the stimulus is stored in the subject's brain. (37) The "irrelevants," by contrast, should not elicit a MERMER.

The real test, however, is the subject's responses to the probes. If the subject has knowledge of the topic at issue, the probes will presumably be noteworthy to the subject, and like the targets, will elicit a MERMER. If the suspect lacks such knowledge, the probes, like the irrelevants, should not elicit a MERMER. (38) By comparing the brainwaves from probes, targets, and irrelevants, Farwell claims his system can determine whether the probes represent information that is known to the subject, even if the subject claims no knowledge of or familiarity with the probe. …

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