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.
A. TYPES OF NTLD
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. …