Traumatic Brain Injury Alters Word Memory Test Performance by Slowing Response Time and Increasing Cortical Activation: An fMRI Study of a Symptom Validity Test

Abstract

The Word Memory Test (WMT) is an established symptom validity test that relies on verbal memory performance to make inferences about “effort.” Previous studies, using a functional MRI (fMRI) adaptation of the WMT with healthy controls, have shown that successful completion of the WMT relies on a widespread network of neural systems associated with high cognitive effort. Additional studies using the same fMRI paradigm with patients with severe traumatic brain injury (TBI) suggest that increased activation of cortical regions associated with cognitive load are recruited to meet the cognitive challenges that the WMT places on a compromised neural system. This study builds on previous findings as a result of highly uncommon circumstances in which fMRI data on the WMT task were made available from the very same individual both 1 year before and 1 year after sustaining a TBI. Interestingly, the effect of TBI did not appear to impair performance on the WMT in terms of standard accuracy measurements, though response times were notably slower. The main fMRI finding was a significantly stronger and more widespread pattern of activation post-injury, particularly in the frontal and parietal brain regions, suggesting that stronger engagement of these networks was necessary to sustain accurate WMT performance compared to pre-injury testing. This unique source of data, together with previous findings, suggests a more complex relationship between effort and performance levels on the WMT than what is commonly assumed.