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

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.

Switching Between Attentional Demands – A Brief Report Comparing Findings from Younger and Older Adults

The increasing relevance to adapt quickly to changes in the environment is contrasted by an inverted U-shaped curve of task-switching abilities over the lifespan. While previous studies most commonly focused on switching between rules, modalities, and attributes, the process of switching between different attentional demands is somehow neglected. Therefore, the present study aims to fill this gap by applying a recently introduced paradigm on switching between attentional demands to younger and older adults. Within the present study, 116 younger adults (age: minmax: 18-30, M=22.31 years, SD=3.17; 85 women) and 93 older adults (age: minmax: 60-89, M=68.29 years, SD=6.18; 15 women) completed the Switching Attentional Demands-task (SwAD-task). The task enables to quantify single-task performance of selective and divided attention, but more important the ability of switching between these demands. Findings indicate faster response times in selective attention than divided attention for both groups. Furthermore, older adults showed longer response times in selective attention, divided attention, as well as switching attention, compared to their younger counterparts. Age-related changes are discussed by considering the frontal ageing hypothesis, processing-speed theory, as well as common factor theories of cognitive ageing. Furthermore, previous neurophysiological findings are taken into account to explain findings at hand.

Hemisphere-specific Parietal Contributions to the Interplay between Working Memory and Attention

To achieve our moment-to-moment goals, we must often keep information temporarily in mind. Yet, this working memory (WM) may compete with demands for our attention in the environment. Attentional and WM functions are thought to operate by similar underlying principles, and they often engage overlapping fronto-parietal brain regions. In a recent fMRI study, bilateral parietal cortex BOLD activity displayed an interaction between WM and visual attention dual-task demands. However, prior studies also suggest that left and right parietal cortices make unique contributions to WM and attentional functions. Moreover, behavioral performance often shows no interaction between concurrent WM and attentional demands. Thus, the scope of reciprocity between WM and attentional functions and the specific contribution that parietal cortex makes to these functions both remain unresolved. Here, we took a causal approach, targeting brain regions that are implicated in shared processing between WM and visual attention, to better characterize how those regions contribute to behavior. We first examined whether behavioral indices of WM and visual search differentially correlate with left and right parietal dual-task BOLD responses. Then, we delivered TMS over fMRI-guided left and right parietal sites during dual-task WM–visual search performance. Only right-parietal TMS influenced visual search behavior, but the stimulation either helped or harmed search depending on the current WM load. Therefore, whereas the left and right parietal contributions were distinct here, attentional and WM functions were codependent. Right parietal cortex seems to hold a privileged role in visual search behavior, consistent with prior findings, but the current results reveal that behavior may be sensitive to the interaction between visual search and WM load only when normal parietal activity is perturbed. The parietal response to heightened WM and attentional demands may therefore serve to protect against dual-task interference.