The construct of working memory and its reliance on dorsolateral prefrontal cortex (DLPFC) have been the focus of many studies in healthy subjects and in clinical populations. However, transfer of knowledge gained from cognitive science studies to clinical applications can be a challenging goal. This scarce cross-dissemination may be partially due to the use of 'tools' that are limited in their ability to generate meaningful information about impairments in clinical groups. To this end, this paper investigates the use of functional near-infrared spectroscopy (fNIRS), which offers unique opportunities for recording neuroactivation. Specifically, we examine measures of the DLPFC hemodynamic response during a working memory task in adults with traumatic brain injury (TBI) and healthy controls. Analysis of hemodynamic measures showed significant differences between the two groups, even without differences in behavioral performance. Additional subtle disparities were linked to levels of performance in TBI and healthy subjects. fNIRS hemodynamic measures may therefore provide novel information to existing theories and knowledge of the working memory construct. Future studies may further define these subtle differences captured by fNIRS to help identify which components affect inter-individual variations in performance and could play a contributing role in the choice and planning of neurorehabilitation interventions targeting working memory.