Novel automaticity index characterizing dual task walking reveals a cognitive ability-related decline in gait automaticity.

Gait automaticity refers to the ability to walk with minimal recruitment of attentional networks typically mediated through the prefrontal cortex (PFC). Reduced gait automaticity is common with aging, contributing to an increased risk of falls and reduced quality of life. A common assessment of gait automaticity is to examine PFC activation via near-infrared spectroscopy (fNIRS) during dual-task (DT), such as walking while performing a cognitive task. However, interpretation of PFC activity without considering task performance could be misleading. For example, greater PFC activation could be interpreted as worse gait automaticity when accompanied by worse DT performance but as compensatory when accompanied by better DT performance. Thus, there is a need to incorporate performance in interpretation of PFC measurements. To address this need, we propose a novel automaticity index as an analytical approach that combines changes in PFC activity with changes in DT performance to quantify gait automaticity. The efficacy of the index was verified in 173 participants (≥65 y/o) who completed DTs with two levels of difficulty while PFC activation was recorded with fNIRS. The two DTs consisted of reciting every other letter of the alphabet while walking over either an even or uneven surface. We found that compared to PFC activation, our novel index better reflected the decrease in automaticity as DT difficulty increases. Furthermore, decreased cognitive ability was related to worse automaticity index, but not PFC activation or DT performance, suggesting that the index is more sensitive to individual characteristics that influence automaticity. In sum, the proposed automaticity index better quantified the between task and individual differences in automaticity by providing a unified measure of gait automaticity that includes both brain activation and performance. This new approach opens exciting possibilities to assess subject-specific deficits and compare rehabilitation outcomes from gait automaticity interventions.