Moderating Effect of White Matter Integrity on Brain Activation during Dual-Task Walking in Older Adults

Using multimodal neuroimaging methods, the current study was designed to examine the relationship between white matter microstructural integrity (WMI) and changes in prefrontal cortex (PFC) oxygenated hemoglobin (HbO 2) during active walking in older adults. Consistent with neural inefficiency, we hypothesized that worse WMI would be associated with a greater increase in PFC HbO 2 from single to dual-task walking in the context of worse or similar gait performance. Fifty-five cognitively healthy older adults (mean age = 74.76 years, 49% women) underwent diffusion tensor imaging (DTI) to derive a whole-brain measure of fractional anisotropy (FA) and functional Near Infrared Spectroscopy (fNIRS), which measured PFC HbO 2 during walking tasks. Gait velocity was assessed using an instrumented walkway. A linear mixed effects model revealed that HbO 2 levels increased from single to dual-task walking (P < 0.01) given the greater cognitive demands inherent in the latter condition. Moreover, WMI moderated the effect of dual tasking on PFC HbO 2 (P < 0.05). Specifically, worse WMI was associated with a larger increase in PFC HbO 2 levels from single to dual-task walking in the context of similar gait velocity. Results suggest that compromised WMI may be a mechanism underlying inefficient brain response to cognitive demands of locomotion.