Interpreting Prefrontal Recruitment During Walking After Stroke: Influence of Individual Differences in Mobility and Cognitive Function

Abstract

Background: Functional near-infrared spectroscopy (fNIRS) is a valuable neuroimaging approach for studying cortical contributions to walking function. Recruitment of prefrontal cortex during walking has been a particular area of focus in the literature. The present study investigated whether task-related change in prefrontal recruitment measured by fNIRS is affected by individual differences in people post-stroke. The primary hypotheses were that poor mobility function would contribute to prefrontal over-recruitment during typical walking, and that poor cognitive function would contribute to a ceiling in prefrontal recruitment during dual-task walking (i.e., walking with a cognitive task). Methods: Thirty-three adults with chronic post-stroke hemiparesis performed three tasks: typical walking at preferred speed (Walk), serial-7 subtraction (Serial7), and walking combined with serial-7 subtraction (Dual-Task). Prefrontal recruitment was measured with fNIRS and quantified as the change in oxygenated hemoglobin concentration (ΔO₂Hb) between resting and active periods for each task. Spatiotemporal gait parameters were measured on an electronic walkway. Stepwise regression was used to assess how prefrontal recruitment was affected by individual differences including age, sex, stroke region, injured hemisphere, stroke chronicity, 10-meter walking speed, balance confidence measured by Activities-specific Balance Confidence (ABC) Scale, sensorimotor impairment measured by Fugl-Meyer Assessment, and cognitive function measured by Mini-Mental State Examination (MMSE). Results: For Walk, poor balance confidence (ABC Scale score) significantly predicted greater prefrontal recruitment (ΔO₂Hb; R ² = 0.25, p = 0.003). For Dual-Task, poor cognitive function (MMSE score) significantly predicted lower prefrontal recruitment (ΔO₂Hb; R ² = 0.25, p = 0.002). Conclusions: Poor mobility function predicted higher prefrontal recruitment during typical walking, consistent with compensatory over-recruitment. Poor cognitive function predicted lower prefrontal recruitment during dual-task walking, consistent with a recruitment ceiling effect. These findings indicate that interpretation of prefrontal recruitment should carefully consider the characteristics of the person and demands of the task.

Keywords: dual-task walking; near-infrared spectroscopy; prefrontal cortex; stroke; walking.

Figure 1

Group average data for the measurements of walking performance during typical walking (Walk) shown in white and dual-task walking (Dual-Task) shown in black. From left to right the graphs show walking speed (A), stride length (B), and step width (C). The error bars denote the standard error. *p < 0.05.

Figure 2

Group average data for the change in prefrontal oxygenated (ΔO₂Hb) and deoxygenated (ΔHHb) hemoglobin concentration from resting period to the active period during single and dual-tasks. From left to right the graphs show ΔO₂Hb (in black) and ΔHHb (in light gray) during typical walking (Walk), serial-7 single task (Serial7), and dual-task walking (Dual-Task). The error bars denote the standard error. *p < 0.05.

Figure 3

Prefrontal oxygenated hemoglobin (ΔO₂Hb) concentration and the measurements of walking performance during typical walking (Walk). The error bars denote the standard error. *p < 0.05. (A) Association between prefrontal recruitment (ΔO₂Hb) during typical walking (Walk) and balance confidence (%) measured by the Activities-specific Balance Confidence (ABC) Scale. (B) Comparison of prefrontal recruitment (ΔO₂Hb) between the High (left) and Low (right) Balance Confidence groups during typical walking (Walk). (C) Comparison of walking performance between the High (left) and Low (right) Balance Confidence groups during typical walking (Walk). The graphs show step width in white, walking speed in light gray, and stride length in black.

Figure 4

Prefrontal oxygenated hemoglobin (ΔO₂Hb) concentration, cognitive performance, and the measurements of walking performance in High (left) and Low (right) Cognitive Function groups during single and dual-tasks. The error bars denote the standard error. *p < 0.05. (A) Comparison of prefrontal recruitment (ΔO₂Hb) between the High (left) and Low (right) Cognitive Function groups during typical walking (Walk) in white, serial-7 single task (Serial7) in light gray, and dual-task walking (Dual-Task) in black. (B) Comparison of serial-7 response rate between the High (left) and Low (right) Cognitive Function groups for serial-7 single task (Serial7) in light gray and dual-task walking (Dual-Task) in black. (C) Comparison of walking performance between the High (left) and Low (right) Cognitive Function groups during dual-task walking (Dual-Task). The graphs show step width in white, walking speed in light gray, and stride length in black.

Figure 5

Association between dual-task cost measured by cognitive performance, and the change in prefrontal oxygenated hemoglobin (ΔO₂Hb_cost) concentration from serial-7 single task (Serial7) to dual-task walking (Dual-Task). Higher task-based increase in prefrontal recruitment (dual-task minus single task) is associated with worse dual-task cost measured by cognitive performance (i.e., a greater drop in serial-7 response rate).

Figure 6

Association between dual-task cost measured by walking speed (Panel A) and stride length (Panel B), and the change in prefrontal oxygenated hemoglobin (ΔO₂Hb_cost) concentration from typical walking (Walk) to dual-task walking (Dual-Task). Higher task-based increase in prefrontal recruitment (dual-task minus single task) is associated with worse dual-task cost measured by walking speed and stride length.