Discriminating Fake From True Brain Injury Using Latency of Left Frontal Neural Responses During Old/New Memory Recognition

Abstract

Traumatic brain injury (TBI) is a major public health concern that affects 69 million individuals each year worldwide. Neuropsychologists report that up to 40% of individuals undergoing evaluations for TBI may be malingering neurocognitive deficits for a compensatory reward. The memory recognition test of malingering detection is effective but can be coached behaviorally. There is great need to develop a novel neural based method for discriminating fake from true brain injury. Here we test the hypothesis that decision making of faking memory deficits prolongs frontal neural responses. We applied an advanced method measuring decision latency in milliseconds for discriminating true TBI from malingerers who fake brain injury. To test this hypothesis, latencies of memory-related brain potentials were compared among true patients with moderate or severe TBI, and healthy age-matched individuals who were assigned either to be honest or faking memory deficit. Scalp signals of electroencephalography (EEG) were recorded with a 32-channel cap during an Old/New memory recognition task in three age- and education-matched groups: honest (n = 12), malingering (n = 15), and brain injured (n = 14) individuals. Bilateral fractional latencies of late positive ERP at frontal sites were compared among the three groups under both studied (Old) and non-studied (New) memory recognition conditions. Results show a significant difference between the fractional latencies of the late positive component during recognition of studied items in malingerers (averaged latencies = 396 ms) and the true brain injured subjects (mean = 312 ms) in the frontal sites. Only malingers showed asymmetrical frontal activity compared to the two other groups. These new findings support the hypothesis that that additional frontal processing of malingering individuals is measurably different from those of actual patients with brain injury. In contrast to our previous reported method using difference waves of amplitudes at frontal to posterior midline sites during new items recognition (Vagnini et al., 2008), there was no significant latency difference among groups during recognition of New items. The current method using delayed left frontal neural responses during studied items reached sensitivity of 80% and specificity of 79% in detecting malingers from true brain injury.

Keywords: EEG; P3; event-related potentials; fractional peak latency; late positive component; malinger; traumatic brain injury.

FIGURE 1

Sample visual stimuli of the Old/New Task. (1) The studied (Old) visual object image (5 s each); (2) Old/New decision on studied and new (non-studied) images.

FIGURE 2

Locations of the frontal electrodes FP1, FP2, F3, and F4 on the 32 channel EEG cap.

FIGURE 3

Group averaged responses during Old items at the electrodes FP1, FP2, F3, and F4. Solid lines represent grand average of ERP responses of honest subjects (blue), malingering subjects (red), and TBI subjects (green) at each electrode site. Dashed lines represent the averaged fractional peak latencies of each group with the same corresponding colors. Asterisks indicate significant results at the electrode. Note that all significant group differences between MAL and true TBI were during memory recognition of studied items.

FIGURE 4

Topographic maps from the three testing groups representing averaged activity from 250 to 400 ms. Group differences were found only during old items. Asterisk indicates significant differences from other groups.

FIGURE 5

Individual’s latency at one left frontal site differentiates malingers with 80% sensitivity and 79% of specificity. Each point represents an individual subject’s P3 latency at a left frontal (F3) site, color coded by subject groups with red representing malingering and green representing brain injured individuals. The solid black line represents the delayed latency threshold at 361 ms.