been used to study affective processes (see Davidson and Irwin, 1999), and there is a burgeoning literature on the neural correlates of cognitive and affective processes that is potentially relevant to psychophysiological detection of deception. Their use to study brain activity associated with deception is only beginning.

PET uses a measure of local blood flow, which invariably accompanies changes in the cellular activity of the brain of normal, awake humans and unanesthetized laboratory animals (for a review, see Raichle, 1987). More recently it has been appreciated that these changes in blood flow are accompanied by much smaller changes in oxygen consumption (Fox and Raichle, 1986; Fox et al., 1988). These changes lead to changes in the actual amount of oxygen remaining in blood vessels at the site of brain activation (i.e., the supply of oxygen is not matched precisely with the demand). Because MRI signal intensity is sensitive to the amount of oxygen carried by hemoglobin (Ogawa et al., 1990), this change in blood oxygen content at the site of changes in brain activity can be detected with MRI (Bandettini et al., 1992; Frahm et al., 1992; Kwong et al., 1992; Ogawa et al., 1992). The detection of these blood-oxygen-level-dependent (BOLD) signals with MRI has become known as functional magnetic resonance imaging or fMRI. Research with fMRI is now providing increasingly detailed maps of human brain function.

Several recent studies provide the beginnings of a scientific underpinning for using fMRI measures for detecting deception. These studies include research on knowledge and emotion. For example, some recent work (e.g., Shah et al., 2001; Tsivilis, Otten, and Rugg, 2001) suggests that seeing familiar names or faces produces distinctively different areas of brain activation than unfamiliar names or faces. In addition, to the extent that deception is associated with increased activation of circuitry associated with anxiety, activation of the amygdala and regions of the prefrontal cortex both reliably accompany certain forms of anxiety (Davidson, 2002). Such studies can help build a theory linking deception to psychological states and specific physiological correlates that might be applied in the future to develop neuroimaging methods for the detection of deception.

Other research is examining the connections between brain activity and phenomena that the polygraph measures. For example, at least five studies combining functional imaging (both PET and fMRI) with simultaneous measurements of the skin conductance response have investigated the brain basis of the conductance response (Critchley et al., 2000; Fredrikson et al., 1998; Raine, Reynolds, and Sheard, 1991; Williams et al., 2000, 2001). These studies show that it reflects a complex interplay in areas of the brain implicated in both emotion regulation and attention. These studies are complemented by parallel studies in patients with well-

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