Functional Neuroimaging of Symptom Validity Testing in Traumatic Brain Injury

The Word Memory Test (WMT) is a commonly used symptom validity test (SVT) that assesses recognition verbal memory. The task has been adapted for use within a functional magnetic resonance imaging (fMRI) paradigm so the neural correlates of WMT activation patterns can be studied. In the current investigation, performance on the delayed recognition subtest of the WMT was examined in two patients who sustained severe TBI and compared to ten healthy controls. The patients underwent comprehensive neuropsychological evaluations and structural MRI. All participants completed two versions of the WMT: full-effort and simulated poor effort conditions. Despite extensive structural brain damage, the fMRI activation patterns during full-effort WMT performance were somewhat similar in the two TBI patients and likewise, somewhat similar to controls. The fMRI activation pattern in both patients demonstrated intact activation of the basic neural structures necessary to perform the WMT. Dissimilar patterns of activation were obtained during the simulated poor effort condition of WMT performance suggesting that fMRI techniques may be sensitive in demonstrating non-credible cognitive performance. The results of our study represent the first fMRI investigation of normal and simulated poor effort SVT performance in individuals with documented brain damage. The implications of fMRI techniques in SVT research and their clinical application are discussed.