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

Rahman, Tabassum Tahmina; Polskaia, Nadia; St-Amant, Gabrielle; Salzman, Talia; Vallejo, Diana Tobón; Lajoie, Yves; Fraser, Sarah Anne · 2021 · Crossref

DOI: 10.3389/fnhum.2021.711054

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Summary

This study investigates whether the type of cognitive demand—discrete versus continuous—modulates attentional load and dual-task costs during walking in young adults. While previous research established that walking is attention-demanding, findings regarding the specific sources of cognitive-motor interference have been inconsistent. The authors hypothesized that continuous tasks, requiring sustained attention, would induce greater prefrontal cortex (PFC) activation and larger performance decrements compared to discrete tasks, which involve short intervals of attention. Nineteen young adults (mean age 21.5 years) performed four cognitive tasks while standing (single cognitive) and while walking at a self-selected pace (dual-task). The discrete tasks included simple reaction time (SRT) and go/no-go inhibition (GNG). The continuous tasks included n-back working memory (NBK) and double number sequence counting (DNS). Prefrontal cerebral hemodynamics were measured using functional near-infrared spectroscopy (fNIRS), specifically tracking changes in oxyhemoglobin (∆HbO2) and deoxyhemoglobin (∆HbR). Behavioral metrics included response accuracy, response time, and gait speed. Behavioral results indicated that accuracy decreased significantly with increasing cognitive demand, with the DNS task yielding the lowest accuracy (81.9%) compared to SRT (100%). Dual-task conditions generally resulted in lower accuracy and slower response times than single-task conditions. Specifically, response times were significantly slower during dual-task SRT and NBK compared to their single-task counterparts. Gait speed was significantly reduced only during the dual-task DNS condition compared to single-task walking, whereas other tasks did not significantly impair walking speed. Neural findings revealed a trend toward increased PFC activation during continuous tasks. A significant three-way interaction for ∆HbO2 showed a trend toward greater activation in the right hemisphere during dual-task DNS compared to single-task walking (p = 0.06). Similarly, ∆HbR analysis indicated a significant interaction, with dual-task DNS showing higher deoxyhemoglobin levels in the right hemisphere compared to single-task conditions. These neural trends suggest that continuous cognitive demands place a higher load on the PFC during walking than discrete tasks. The study concludes that categorizing tasks by attentional demand (discrete vs. continuous) helps clarify dual-task interference, with continuous tasks eliciting greater neural engagement and specific motor costs, particularly in gait speed.

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• neuro workload indices