Using functional near-infrared spectroscopy (fNIRS) in the assessment of cognitive motor interference in post-stroke patients

Introduction/Background Pre-frontal cortex (PFC) activity during dual task (DT) condition in stroke patients remains unclear. Functional near-infrared spectroscopy (fNIRS) is a functional neuroimaging technique for studying cortical activity. The purpose of this study was to evaluate the hemodynamic activity of the PFC in two DT conditions in post-stroke patients. Material and method Stroke patients were instructed to perform a cognitive task (n-back test) while continuously walking. They were evaluated in DT low (n-1 back) and high (n-2 back) cognitive load. fNIRS recorded bilateral PFC activity and GAITRite measured gait parameters in these two DT conditions. Cognitive performance was evaluated by the number of answers, the number of correct answers and the error percentage. The main endpoint was the DT cost, and we compared the change in oxygenated hemoglobin (an indicator of the changes in PFC activation) between the DT high and DT low. Results Eleven stroke patients (8 men and 3 women; mean age, 64.2 ± 19.5 years; range, 28–87 years) were included in the study. The DT cost was higher in DT n-2 (82.1% ± 15.6) compared with DT n-1 (61.2% ± 38.6), P  = 0.007. There was no decline of spatiotemporal gait parameters with the increasing of cognitive load ( P  u003e 0.05) and no difference for the number of answers in DT high versus low cognitive load ( P  u003e 0.05). The number of correct answers was lower during DT high (3 ± 2.4) versus DT low (7.8 ± 3.6), P  = 0.0015; and the error percentage was higher during DT high (62.3 ± 23.2) versus low condition (24.4 ± 12.9), P  = 0.0001. Conclusion There was a greater increase bilateral PFC activity during DT high versus DT low. The increasing DT cost allowed to maintain spatiotemporal gait parameters in DT high and led to a degradation of the cognitive performance. During DT, PFC activation might prioritize gait performances in stroke patients when the cognitive load is high.