Prefrontal over-activation during walking in people with mobility deficits: Interpretation and functional implications

Abstract

Background: Control of walking by the central nervous system includes contributions from executive control mechanisms, such as attention and motor planning resources. Executive control of walking can be estimated objectively by recording prefrontal cortical activity using functional near infrared spectroscopy (fNIRS).

Objective: The primary objective of this study was to investigate group differences in prefrontal/executive control of walking among young adults, older adults, and adults post-stroke. Also assessed was the extent to which walking-related prefrontal activity fits existing cognitive frameworks of prefrontal over-activation.

Methods: Participants included 24 adults post-stroke with moderate to severe walking deficits, 15 older adults with mild gait deficits, and 9 young healthy adults. Executive control of walking was quantified as oxygenated hemoglobin concentration in the prefrontal cortex measured by fNIRS. Three walking tasks were assessed: typical walking, walking over obstacles, and walking while performing a verbal fluency task. Walking performance was assessed by walking speed.

Results: There was a significant effect of group for prefrontal activity (p < 0.001) during typical and obstacles walking tasks, with young adults exhibiting the lowest level of prefrontal activity, followed by older adults, and then adults post-stroke. In young adults the prefrontal activity during typical walking was much lower than for the verbal fluency dual-task, suggesting substantial remaining prefrontal resources during typical walking. However, in older and post-stroke adults these remaining resources were significantly less (p < 0.01). Cumulatively, these results are consistent with prefrontal over-activation in the older and stroke groups, which was accompanied by a steeper drop in walking speed as task complexity increased to include obstacles (p < 0.05).

Conclusions: There is a heightened use of prefrontal/executive control resources in older adults and post-stroke adults during walking. The level of prefrontal resource utilization, particularly during complex walking tasks like obstacle crossing, may approach the ceiling of available resources for people who have walking deficits. Prior cognitive research has revealed that prefrontal over-activation combined with limited prefrontal resources can lead to poor cognitive performance. The present study suggests a similar situation influences walking performance. Future research should further investigate the extent to which prefrontal over-activation during walking is linked to adverse mobility outcomes.

Keywords: Ambulation; Elderly; Near-infrared spectroscopy; Prefrontal cortex; Stroke.

Published by Elsevier B.V.

Figures

Fig. 1. Group mean prefrontal activity by walking task

Prefrontal activity for each group, quantified by fNIRS as ΔO2Hb, is shown for the typical, obstacles, and verbal walking tasks. Error bars indicated standard error of the mean. Black lines are from the early phase of each walking task and gray lines are from the late phase. Young, elderly, and stroke groups are shown in Panels A, B and C, respectively. Significant differences in elderly group relative to young are shown with *. Significant differences in the stroke group relative to elderly are shown with †. Significant differences in the stroke group relative to young are shown with ‡.

Figure 2. Stroke subgroup mean prefrontal ΔO2Hb by walking task

Prefrontal activity for subgroups of post-stroke participants, quantified by fNIRS as ΔO2Hb, is shown for the typical (squares) and obstacles (triangles) walking tasks. Error bars indicate standard error of the mean. Subgroups were defined based on lower extremity Fugl-Meyer Assessment score (FMA). The asterisk indicates a significant main effect of subgroup.

Figure 3. Change in walking speed for obstacles task

Percent change in walking speed relative to typical walking for the obstacles task. Error bars are standard deviation. All within-group and between-group comparisons of speed were statistically significant at p