News
fMRI might help differentiate MDD and bipolar disorder
Major depressive disorder and bipolar disorder appear to be associated with different underlying brain structures.
Alternative Modalities
Given the pitfalls inherent with external physiologic measures for lie detection, additional modalities that bypass measurement of ANS-governed responses have been sought. Indeed, the integration and combination of more comprehensive modalities has come to be named the forensic credibility assessment.
Functional MRI
Beginning in 1991, researchers began using fMRI to see real-time perfusion changes in areas of the cerebral cortex between times of rest and mental stimulation.26 This modality provides a noninvasive technique for viewing which specific parts of the brain are stimulated during activity. When someone is engaged in active deception, the dorsolateral prefrontal cortex has greater perfusion than when the patient is engaged in truth telling.28 Since fMRI involves imaging for evaluation of the central nervous system, it avoids the potential inaccuracies that can be seen in some subjects with autonomic irregularities. In fact, fMRI may have superior sensitivity and specificity for lie detection compared with that of conventional polygraphy.29
Significant limitations to the use of fMRI include the necessity of expensive specialized equipment and trained personnel to operate the MRI. Agencies that use polygraph examinations may be unwilling to make such an investment. Further, subjects with metallic foreign bodies or noncompatible medical implants cannot undergo the MRI procedure. Finally, there have been bioethical and legal concerns raised that measuring brain activity during interrogation may endanger “cognitive freedom” and may even be considered unreasonable search and seizure under the Fourth Amendment to the US Constitution.30 However, fMRI—like polygraphy—can only measure the difference between brain perfusion in 2 states. The idea of fMRI as “mind reading” is largely a misconception.31
Electroencephalography
Various EEG modalities have received increased interest for lie detection. In EEG, electrodes are used to measure the summation of a multitude of postsynaptic action potentials and the local voltage gradient they produce when cortical pyramidal neurons are fired in synchrony.32 These voltage gradients are detectable at the scalp surface. Shortly after the invention of EEG, it was observed that specific stimuli generated unique and predicable changes in EEG morphology. These event-related potentials (ERP) are detectable by scalp EEG shortly after the stimulus is given.33
ERPs can be elicited by a multitude of sensory stimuli, have a predictable and reproducible morphology, and are believed to be a psychophysiologic correlate of mental processing of stimuli.34 The P300 is an ERP characterized by a positive change in voltage occurring 300 milliseconds after a stimulus. It is associated with stimulus processing and categorization.35 Since deception is a complex cognitive process involving recognizing pertinent stimuli and inventing false responses to them, it was theorized that the detection of a P300 ERP during a patient interview would mean the patient truly recognizes the stimulus and is denying such knowledge. Early studies performed on P300 had variable accuracy for lie detection, roughly 40% to 80%, depending on the study. Thus, the rate of false negatives would increase if the subjects were coached on countermeasures, such as increasing the significance of distractor data or counting backward by 7s.36,37 Later studies have found ways of minimizing these issues, such as detection of a P900 ERP (a cortical potential at 900 milliseconds) that can be seen when subjects are attempting countermeasures.38
Another technique for increasing accuracy in EEG-mediated lie detection is measurement of multifaceted electroencephalographic response (MER), which involves a more detailed analysis of multiple EEG electrode sites and how the signaling changes over time using both visual comparison of multiple trials as well as bootstrap analysis.37 In particular, memory- and encoding-related multifaceted electroencephalographic response (MERMER) using P300 coupled with an electrically negative impulse recorded at the frontal lobe and phasic changes in the global EEG had superior accuracy than P300 alone.37
The benefits of EEG compared with that of fMRI include large reductions in cost, space, and restrictions for use in some individuals (EEG is safe for virtually all patients, including those with metallic foreign bodies). However, like fMRI, EEG still requires trained personnel to operate and interpret. Also, it has yet to be tested outside of the laboratory.
