fNIRS-based investigation of the Stroop task after TBI

To evaluate neural changes during a Stroop task among individuals with TBI using functional near-infrared spectroscopy (fNIRS). Thirteen healthy controls and 14 patients with moderate to severe TBI were included in this study. Oxygenated hemoglobin (HbO) was recorded every tenth of a second using a 52-channel fNIRS unit. Data were acquired using a block design during a Stroop task (i.e., Condition A = Dot Color Naming, Condition B = Incongruent Condition). Visual stimuli were presented on a computer monitor. Behaviorally, response accuracy was similar between groups for condition A, but the TBI group made more errors than the control group during condition B. During condition A, the patient group demonstrated significant increases in HbO within bilateral frontal regions compared to controls (p < 0.01). When examining the Stroop interference effect (B-A), controls showed increased HbO in bilateral frontal lobes and left inferior parietal region suggesting increased neural response to increased cognitive demand, whereas no differences were detected among the TBI group (p < 0.05). No between group differences in latency of HbO response was observed during either condition. While the TBI group performed as accurately as controls on the simpler dot color naming condition of the Stroop task, neural activity was greater within the frontal lobes during this relatively simple task among the TBI group suggesting neural inefficiency. Furthermore, the spatial distribution of neural activity related to the interference effect was not different among patients, suggesting the neural demand for the simpler task was comparable to that of the more cognitive demanding task among the TBI sample. The results suggest that fNIRS can identify frontal lobe inefficiency in TBI commonly observed with fMRI.