Distinct fNIRS-Derived HbO₂ Trajectories during the Course and over Repeated Walking Trials under Single-and Dual-Task Conditions: Implications for Within Session Learning and Prefrontal Cortex Efficiency in Older Adults

Background: Neural trajectories of gait are not well established. We determined two distinct, clinically relevant neural trajectories, operationalized via functional near-infrared spectroscopy (fNIRS) HbO₂ measures in the prefrontal cortex (PFC), under Single-Task-Walk (STW), and Dual-Task-Walk (DTW) conditions. Course trajectory assessed neural activity associated with attention during the course of a walking task; the second trajectory assessed neural activity associated with learning over repeated walking trials. Improved neural efficiency was defined as reduced PFC HbO 2 after practice. Methods: Walking was assessed under STW and DTW conditions. fNIRS was utilized to quantify HbO₂ in the PFC while walking. Burst measurement included three repeated trials for each experimental condition. The course of each walking task consisted of six consecutive segments. Results: Eighty-three nondemented participants (mean age = 78.05 ± 6.37 years; %female = 49.5) were included. Stride velocity (estimate =-0.5259 cm/s, p = <.0001) and the rate of correct letter generation (log estimate of rate ratio =-0.0377, p <.0001) declined during the course of DTW. In contrast, stride velocity (estimate = 1.4577 cm/s, p <.0001) and the rate of correct letter generation (log estimate of rate ratio = 0.0578, p <.0001) improved over repeated DTW trials. Course and trial effects were not significant in STW. HbO₂ increased during the course of DTW (estimate = 0.0454 μM, p <.0001) but declined over repeated trials (estimate =-0.1786 μM, p <.0001). HbO₂ declined during the course of STW (estimate =-.0542 μM, p <.0001) but did not change significantly over repeated trials. Conclusion: We provided evidence for distinct attention (course) and learning (repeated trials) trajectories and their corresponding PFC activity. Findings suggest that learning and improved PFC efficiency were demonstrated in one experimental session involving repeated DTW trials.