Walking while Performing Working Memory Tasks Changes the Prefrontal Cortex Hemodynamic Activations and Gait Kinematics

Abstract

Background: Increasing evidence suggests that walking while performing a concurrent task negatively influences gait performance. However, it remains unclear how higher-level cognitive processes and coordination of limb movements are altered in challenging walking environments. This study investigated the influence of cognitive task complexity and walking road condition on the neutral correlates of executive function and postural control in dual-task walking.

Methods: Twenty-four healthy young adults completed a series of overground walks with three walking road conditions (wide, narrow, with obstacles) with and without the concurrent n-back working memory tasks of two complexity levels (1-back and 3-back). Prefrontal brain activation was assessed by functional near-infrared spectroscopy. A three-dimensional motion analysis system was used simultaneously to measure gait performance and lower-extremity kinematics. Repeated measures analysis of variance were performed to examine the differences between the conditions.

Results: In comparison with standing still, participants showed lower n-back task accuracy while walking, with the worst performance from the road with obstacles. Spatiotemporal gait parameters, lower-extremity joint movements, and the relative changes in oxygenated hemoglobin (HbO) concentration levels were all significantly different across the task complexity and walking path conditions. While dual-tasking participants were found to flex their hips and knees less, leading to a slower gait speed, longer stride time, shorter step length, and greater gait variability than during normal walking. For narrow-road walking, smaller ankle dorsiflexion and larger hip flexion were observed, along with a reduced gait speed. Obstacle negotiation was mainly characterized by increased gait variability than other conditions. HbO levels appeared to be lower during dual-task walking than normal walking. Compared to wide and obstacle conditions, walking on the narrow road was found to elicit a smaller decrement in HbO levels.

Conclusion: The current study provided direct evidence that, in young adults, neural correlates of executive function and dynamic postural control tend to be altered in response to the cognitive load imposed by the walking environment and the concurrent task during ambulation. A shift of brain activation patterns between functionally connected networks may occur when facing challenging cognitive-motor interaction.

Keywords: NIRS; cognitive; dual task; gait; kinematic; n-back; obstacle.

FIGURE 1

Presentation of (A) hip, (B) knee, and (C) ankle joint kinematics from the right side of 24 participants as ensemble-averaged waveforms for different combinations of cognitive task complexity and walking road condition. The results obtained from 1-back and 3-back task are combined and showed as DT for clarity.

FIGURE 2

Summary behavior outcomes of the n-back WM tasks for (A) accuracy, and (B) correct RT in all combinations of cognitive task complexity and walking road condition. Error bars represent ±1 SE. An asterisk (^∗) denotes a significant difference (p < 0.05) between the 1-back and 3-back task under the same walking road condition. Under the same cognitive task complexity, a significant difference (p < 0.05) between the target road condition and the stand/wide/narrow road condition is denoted by the symbol S/W/N, respectively.

FIGURE 3

Summary results of spatiotemporal gait parameters for (A) average gait speed, (B) average stride time, (C) average step length, (D) variability of gait speed, (E) variability of stride time, and (F) variability of step length in all combinations of cognitive task complexity and walking road condition. Error bars represent ±1 SE. Under the same walking road condition, a significant difference (p < 0.05) between the target cognitive task complexity and l-back/3-back task is denoted by the symbol asterisk (^∗)/pound (#), respectively. Under the same cognitive task complexity, a significant difference (p < 0.05) between the target road condition and the wide/narrow road condition is denoted by the symbol W/N, respectively.

FIGURE 4

Presentation of changes in the relative concentration level of HbO during (A) normal walking, (B) dual-tasking with the 1-back task, and (C) dual-tasking with the 3-back task from pre-test quiet standing (0–20 s), countdown block (20–25 s), test block (25–85 s), and post-test quiet standing (85–105 s). Graphs are showed as ensemble-averaged waveforms from 24 participants for different combinations of cognitive task complexity and walking road condition.