The Study On Applying Event-related Potentials With Judge Figures Difference To Detect Malingered Cognitive Impairment

【Background】Cognitive deficits are common manifestation about traumatic brain injury patients as in traffic accidents or worker's compensation cases, which is directly correlated with the evaluation of disability rating in forensic practices. A considerable number of individuals are thought to be more likely to feign neuropsychological impairment because of their potential monetary incentive. So it's essential to distinguish honest from feigned performance. Judicial doctors usually judge qualitatively on the basis of their experiences which are lower sensitive. Therefore it is significantly pragmatic to investigate other, more covert, objective measures to distinguish honest from feigned performance.Event-related potentials (ERP) is averaged electroencephalography signals recorded from the scalp that reflect activity underlying a time-locked perceptual or cognitive event, which is less affected by motivational factors. An increasing attention has been given to this area recently. The P300, MFN, CNV components has been reported to be associated with cognition process about malingering. So it is theoretically feasible to detect malingered cognitive deficit applying ERP measure. And develop a convenient and standardized ERP measure for detecting malingering could provide objective quantization indexes for forensic practices.【Objectives】According to the theory of Binominal Forced-Choice Digit Memory Test (BFDMT) and ERP, some figures difference judgment stimulus paradigms were developed. These studies were to investigate the features of ERP elicited by these paradigms in honest (HON) responders, malingering (MAL) responders and traumatic brain injury (TBI) group.【Methods】EEG were recorded on-line in 40 healthy volunteers(HON and MAL group) and 20 patients with TBI (TBI group) by Neuroscan's ERP after their completing Binominal Forced - Choice Digit Memory Test. Then their wave amplitude and latent period of event related potential components, easy score, difficult score and quotient about BFDMT were obtained.【Results】(1) There was a significant difference between groups for BFDMT data (P<0.01). Post hoc comparisons indicated that for BFDMT MAL had a significantly lower score (total score=8.8, easy score=4.8, difficult score=4.0 ) and a significantly higher quotient (46.6) than HON and TBI (P<0.01). (2) The accuracy rate for identical figures about HON and TBI are all 98.2%, and MAL had a lower accuracy rate compared to HON and TBI (P<0.01). There was a significant difference in accuracy rate for uncorrelated and similar figures, and that HON had a highest accuracy rate compared to TBI and MAL, and MAL had a lowest accuracy rate. (3) The components of ERP elicited by figures difference judgment paradigm in responders in three groups all included N1, P2, N2 P3 and N3. In all groups the N3 latency for similar figures were longer compared to identical figures, and the N2, P3, N3 latency for irrelevant figures were longer than identical figures, and the N2, P3 latency were longer than similar figures (P<0.05). (4) There was a significant difference for N2, P3 and N3 latency and amplitude between three groups. The N2 amplitude for identical figures stimulus of MAL were higher than HON (P<0.05), and the P3 latency were longer than HON (P<0.01) but shorter than TBI (P<0.05), and the P3 amplitude were lower than HON (P<0.05). The N3 latency were shorter than TBI (P<0.01) but no significant difference compared to HON. The N2 latency for irrelevant figures of MAL were no significant difference compared to HON but shorter than TBI, and the P3 latency were longer than HON but shorter than TBI (P<0.01), and the P3 amplitude were lower than HON (P<0.05). The N3 latency were longer than HON but shorter than TBI, and the N3 amplitude were lower than HON (P<0.05). The P3 latency for similar figures of MAL were longer than HON (P<0.01), and the N3 latency were shorter than HON and TBI (P<0.01), and the N3 amplitude were lower than HON (P<0.01). (5) The 2D topographical map across the scalp of N3 shows that when comparing activity within each figure, irrelevant figures had stronger activity than identical figures and the identical figures had stronger activity than similar figures. When comparing activity within each figure, HON had stronger activity than MAL and MAL had stronger activity than TBI. (6) Most of point (Cz,FCz,CPz,Fz,FC3,FC4,C3,C4,P3,P4) had obtained the manifest ERP wave by the figures difference judgment stimulus sequences, and the most stabile registration point is Cz,FCz,CPz. ERP components about N1, P2, N2, P3 and N3 components that presented at approximately 90~470ms respectively. The N1, P2 latency and amplitude which were found to be good indicators to evaluate individuals conscientiously perceive the figures or not were no significant difference within three groups, while there was a significant difference for the amplitude and latency of N3 component, which was demonstrated as a reliable indicator for malingering detection.