Cortical thickness moderates intraindividual variability in prefrontal cortex activation patterns of older adults during walking

Objective: Increased intraindividual variability (IIV) in behavioral and cognitive performance is a risk factor for adverse outcomes but research concerning hemodynamic signal IIV is limited. Cortical thinning occurs during aging and is associated with cognitive decline. Dual-task walking (DTW) performance in older adults has been related to cognition and neural integrity. We examined the hypothesis that reduced cortical thickness would be associated with greater increases in IIV in prefrontal cortex oxygenated hemoglobin (HbO₂) from single tasks to DTW in healthy older adults while adjusting for behavioral performance. Method: Participants were 55 healthy community-dwelling older adults (mean age = 74.84, standard deviation (SD) = 4.97). Structural MRI was used to quantify cortical thickness. Functional near-infrared spectroscopy (fNIRS) was used to assess changes in prefrontal cortex HbO₂ during walking. HbO₂ IIV was operationalized as the SD of HbO₂ observations assessed during the first 30 seconds of each task. Linear mixed models were used to examine the moderation effect of cortical thickness throughout the cortex on HbO₂ IIV across task conditions. Results: Analyses revealed that thinner cortex in several regions was associated with greater increases in HbO₂ IIV from the single tasks to DTW (ps < .02). Conclusions: Consistent with neural inefficiency, reduced cortical thickness in the PFC and throughout the cerebral cortex was associated with increases in HbO₂ IIV from the single tasks to DTW without behavioral benefit. Reduced cortical thickness and greater IIV of prefrontal cortex HbO₂ during DTW may be further investigated as risk factors for developing mobility impairments in aging.