Frontoparietal activity during deceptive responses in the P300-based guilty knowledge test: an sLORETA study.

The cortical source activity during the P300-based guilty knowledge test (GKT) conducted using Korean sentences was investigated. Thirty male students performed a guilty or an innocent scenario, and then underwent an electroencephalogram test. The stimuli consisted of target, probe, and irrelevant stimuli that were presented visually. A target stimulus is a task-relevant stimulus that is presented rarely, attracts subjects' attention, and induces a P300 wave. A probe stimulus, also presented rarely, contains crime-relevant information that induces P300 in a guilty subject. A guilty subject would be also attentive to the probe stimulus as to the target stimulus. An irrelevant stimulus is not related to the task or to the crime, and is frequently presented. Event-related potential (ERP) data showed a marked difference between the guilty and innocent groups. Compared to irrelevant stimuli, the probe stimulus elicited larger P300 amplitude in the bilateral frontoparietal region in the guilty group. However, this pattern was not observed in the innocent group. Standardized low-resolution electromagnetic tomography (sLORETA) analysis showed significant activation increases for the probe stimulus in the guilty group. It appears that the guilty and innocent groups use different cognitive mechanisms when processing the crime-relevant sentence. With regards to the cortical activity in response to the probe stimulus, the frontal activation for verb elements seems to reflect a working memory process, episodic memory retrieval, and response inhibition, while parietal activation for complement (adverb) and object (noun) elements seems to reflect selective attention and target discrimination. To our knowledge, this is the first research to examine the cortical source of the ERP evoked by the P300-based GKT using separate Korean sentence elements.