Utilization of central nervous system resources for preparation and performance of complex walking tasks in older adults

Abstract

Introduction: Walking in the home and community often involves performance of complex walking tasks. Understanding the control of such tasks is crucial to preserving independence and quality of life in older adults. However, very little research has been conducted in this area. Here, we assess the extent to which two measures of central nervous system (CNS) activity are responsive to the challenges posed by preparation and performance of complex walking tasks. Prefrontal cortical activity was measured by functional near-infrared spectroscopy (fNIRS) and sympathetic nervous system arousal was measured by skin conductance level (SCL).

Materials and methods: Sixteen older men and women (age: 77.2 ± 5.6 years) with mild mobility deficits participated in this study. Participants walked at their preferred speed without distractions along an unobstructed, well-lit course (control task) and also walked on the same course under five separate challenging conditions: performing a cognitive verbal fluency task (verbal task), dim lighting (dim task), carrying a tray (carry task), negotiating obstacles (obstacles task) and wearing a weighted vest (vest task). Mean prefrontal activation and SCL were calculated during the preparation and performance phases of each task. Gait spatiotemporal measurements were acquired by an instrumented gait mat.

Results: Prefrontal cortical activity and SCL were elevated during the preparation phase of complex walking tasks relative to the control task. During the performance phase, prefrontal activity remained elevated to a similar level as during task preparation. In contrast, SCL continued to increase beyond the level observed during task preparation. A larger increase in prefrontal activity was found to be linked to preserved quality of gait during complex walking tasks.

Discussion: These findings indicate that availability and utilization of CNS resources are important for optimizing performance of complex walking tasks in older adults.

Keywords: aging; motor control; near infrared spectroscopy; skin conductance; walking.

FIGURE 1

Exemplar data demonstrating task-dependent differences in tissue oxygenation index (TOI). Prefrontal cortical activation, as indicated by TOI, for one study participant. Data are shown for walking along an unobstructed, well-lit pathway (control task; black solid line), walking while carrying a tray (carry task; dotted line), walking in dim lighting (dim task; gray solid line) and walking while performing a verbal fluency task (verbal task; dashed line). The participant is standing still for a short period of time at the start of the trial (preparation phase) and then walks at preferred speed (performance phase).

FIGURE 2

Increase in prefrontal activation for complex tasks relative to preparation for control task. Gray bars indicate the average percentage increase in prefrontal activation during the preparation phase of each complex walking task relative to preparation for the control task. Significant changes are shown by an asterisk. Black bars indicate the percentage increase in prefrontal activation during the performance phase of each complex walking task relative to preparation for the control task. Significant changes are shown by a dagger. Error bars indicate group standard error.

FIGURE 3

Exemplar data demonstrating task-dependent differences in skin conductance level (SCL). Sympathetic nervous system (SNS) arousal, as indicated by SCL, for one study participant. Data are shown for walking along an unobstructed, well-lit pathway (control task; black solid line), walking while carrying a tray (carry task; dotted line), walking in dim lighting (dim task; gray solid line) and walking while performing a verbal fluency task (verbal task; dashed line). The participant is standing still for a short period of time at the start of the trial (preparation phase) and then walks at preferred speed (performance phase).

FIGURE 4

Increase in skin conductance level (SCL) for complex tasks relative to preparation for control task. Gray bars indicate the average percentage increase in SCL during the preparation phase of each complex walking task relative to preparation for the control task. Significant changes are shown by an asterisk. Black bars indicate the percentage increase in SCL during the performance phase of each complex walking task relative to preparation for the control task. Significant changes are shown by a dagger. Significant within-task differences (preparation versus performance) are shows by a double dagger. Error bars indicate group standard error.