An fNIRS Investigation of Discrete and Continuous Cognitive Demands During Dual-Task Walking in Young Adults

Abstract

Introduction: Dual-task studies have demonstrated that walking is attention-demanding for younger adults. However, numerous studies have attributed this to task type rather than the amount of required to accomplish the task. This study examined four tasks: two discrete (i.e., short intervals of attention) and two continuous (i.e., sustained attention) to determine whether greater attentional demands result in greater dual-task costs due to an overloaded processing capacity. Methods: Nineteen young adults (21.5 ± 3.6 years, 13 females) completed simple reaction time (SRT) and go/no-go (GNG) discrete cognitive tasks and n-back (NBK) and double number sequence (DNS) continuous cognitive tasks with or without self-paced walking. Prefrontal cerebral hemodynamics were measured using functional near-infrared spectroscopy (fNIRS) and performance was measured using response time, accuracy, and gait speed. Results: Repeated measures ANOVAs revealed decreased accuracy with increasing cognitive demands (p = 0.001) and increased dual-task accuracy costs (p < 0.001). Response times were faster during the single compared to dual-tasks during the SRT (p = 0.005) and NBK (p = 0.004). DNS gait speed was also slower in the dual compared to single task (p < 0.001). Neural findings revealed marginally significant interactions between dual-task walking and walking alone in the DNS (p = 0.06) and dual -task walking compared to the NBK cognitive task alone (p = 0.05). Conclusion: Neural findings suggest a trend towards increased PFC activation during continuous tasks. Cognitive and motor measures revealed worse performance during the discrete compared to continuous tasks. Future studies should consider examining different attentional demands of motor tasks.

Keywords: cognitive demand; continuous cognitive task; discrete cognitive task; dual task; fNIRS (functional near infrared spectroscopy); overground walking; prefrontal cortex (PFC); younger adults.

Figure 1

(A) Participant wearing the fNIRS device. (B) fNIRS optode configuration. (C) fNIRS optode configuration mapped onto an MRI scan. Rx1 and Rx2 are detectors; Tx1 through Tx8 are channels. (D) Fully instrumented participant with fNIRS, headphones, and voice recorder.

Figure 2

Experimental protocol for a run. B = baseline (fNIRS quiet standing); R = rest; SC = single cognitive (SRT, GNG, NBK or DNS in a randomized run order while standing); SM = single motor (usual walking); DT = dual-task (cognitive task and walking).

Figure 3

fNIRS optode configuration mapped onto an MRI scan. MRI demonstrates that all the optodes and receivers on the fNIRS are positioned over the right and left Brodmann area 10. R1 and R2 represent detectors; the green numbers 1 through 8 are the fNIRS infrared light emitters.

Figure 4

Mean changes in accuracy rates (%) across (A) single (SC) and dual (DT) tasks (F_{(1, 18)} = 15.42, p = 0.001, ${\eta }_{\text{p}}^2$ = 0.46). (B) Simple reaction time (SRT), go/no-go (GNG), n-back (NBK) and double number sequence (DNS) accuracy rates across cognitive demands (F_{(3, 54)} = 63.82, p < 0.001, ${\eta }_{\text{p}}^2$ = 0.78). Error bars represent standard deviation and (*) denotes a significant difference (p < 0.05).

Figure 5

Mean changes in response time across single cognitive (SC) and dual-tasks (DT) with increasing cognitive demand (N = 19, F_{(2, 36)} = 4.1, p = 0.026, ${\eta }_{\text{p}}^2$ = 0.18). Error bars represent standard deviation and (*) denotes a significant difference (p < 0.05).

Figure 6

Mean changes in gait speed across single motor (SM) and dual-task (DT) blocks (N = 19, F_{(3, 54)} = 5.579, p = 0.002, ${\eta }_{\text{p}}^2$ = 0.24). Error bars represent standard deviation and (*) denotes a significant difference (p < 0.05).

Figure 7

Left (A) and right (B) mean hemispheric changes in cerebral oxygenation (ΔHbO₂) between single motor (SM) and dual-task (DT) blocks. The right hemisphere consists of channels 1–4 and the left hemisphere consists of channels 5–8. This data is the group average post-processed with baseline subtraction, filtering, and outlier correction.