HbO2 Variability During Walking and Walking While Talking in Older Adults
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Evidence that mobility and cognition are interrelated is robust, especially in older adults. Functional neuroimaging studies of gait have shown that the prefrontal cortex (PFC) and related neural circuitry sub-serve gait, notably under attention-demanding dual-task conditions. Although time course analyses have been reported, functional neuroimaging studies of gait to date have focused on average patterns of neural activity. Emerging neuroscience research suggests that variability of neural activity may also have intrinsic meaning. As such, examining variability of neural activity during gait may offer novel insights into the inherently dynamic nature of the brain. The objectives of this study were 1) to compare oxygenated hemoglobin (HbO2) variability in the PFC under single-task (normal walking; NW) and dual-task (walking while talking; WWT) gait conditions and 2) to determine the association between PFC HbO2 variability and gait performance in older adults. Functional near-infrared-spectroscopy (fNIRS) was used to assess PFC HbO2 during locomotion in 274 cognitively healthy older adults (mean age = 75.88 years; female = 55.80%). HbO2 variability was operationalized as the standard deviation of HbO2 values across six continuous trial epochs during NW and WWT. Reliability and validity for this gait paradigm have been previously established. Linear mixed effect models revealed significantly higher PFC HbO2 variability during WWT compared to NW (estimate = -.12; 95%CI = -.14 to -.10; p<.001). Higher PFC HbO2 variability was also associated slower gait velocity (estimate = -10.69; 95%CI = -18.91 to 2.48; p = .011) and higher stride length variability (estimate = 4.11; 95%CI = 1.66 to 6.56; p = .001) during WWT. The analyses controlled for gender, age, education, disease comorbidity, and mean HbO2 values. Our results are in line with accumulating evidence from studies of behavioral variability that demonstrate increased variance in cognitive or gait performance during tasks requiring greater executive control. In addition, our results provide first evidence of the relationship between PFC HbO2 variability and gait performance. These initial findings encourage the future use of variability measures to examine functional neural correlates of gait in older adults.