Greater Mental Fatigability Moderates the Relationship Between Prefrontal Cortex Activation and Gait Speed in Dual-Task Walking

Slowing in gait speed is associated with reduced mobility and patterns of prefrontal cortex (PFC) activation influence this relationship, reflecting reduced automaticity of walking. Loss of automaticity may be overcome by neural compensation that occurs in the PFC to maintain gait. Higher PFC activation while walking in older adults may indicate an overreliance on cognitive resources and can help maintain gait speed but the ability to maintain gait speed may be lost once compensatory recruitment reaches its limit. Various pathological factors are known to moderate this relationship and reduce the extent to which the PFC can be recruited, resulting in inadequate cognitive resources to maintain gait speed. This research addresses how fatigability, a whole-body measure of susceptibility to fatigue, fits into this framework. Maintaining faster gait speed is expected to require more PFC compensation in those with more physical and mental fatigability vs. those with less. This analysis combined cohorts from three University of Pittsburgh mobility studies (N=114) to investigate the effect of perceived physical and mental fatigability as measured through the Pittsburgh Fatigability Scale on the relationship between PFC activation and gait speed during single- and dual-task walking. Multivariate linear regression models assessed the association of PFC activation, level of fatigability, and other health factors with gait speed across those with more or less physical and mental fatigability across both task conditions. There was no significant association between PFC activation and gait speed across those with more or less perceived physical fatigability. In the single-task v condition, having more perceived mental fatigability led to an association between higher PFC activation and faster gait speed in the single-task condition, although this association was attenuated by the inclusion of age. This same association was found in the dual-task models (ß = 0.030 (0.005 – 0.055)) and remained significant even after the inclusion of age in the model (ß = 0.026 (0.003 – 0.49). These findings indicate that having more mental fatigability may reduce automaticity of walking which requires additional PFC compensation to combat. Public health interventions can benefit from these findings through applying early interventions to reduce higher mental fatigability