The effect of distraction and feedback on prefrontal cortex activity and balance in middle-aged adults: A functional near-infrared spectroscopy pilot study

Maintaining balance while simultaneously performing other tasks is common during everyday activities. However, this dual-tasking (DT) divides attention and increases cognitive demand, which can be detrimental to stability in older adults. It is unknown if the focus of attention influences how a dual-task affects balance and whether this is detectable in middle-aged adults. This study investigates the effect of dual-task and attentional focus on prefrontal cortex (PFC) activity in young (YA) and middle-aged (MA) adults using functional-near infrared spectroscopy. Blood oxygen level of the PFC was measured during a quiet standing cognitive-motor dual-task where MA (n = 15, mean age 57.2 ± 4.8 years, 5 female) and YA (n = 20, mean age 24.9 ± 4.7 years, 9 female) stood on a forceplate while either fixating their gaze on a target ('fixed') or viewing their real-time postural oscillations in the anteroposterior direction ('sway') with and without serial 7 subtractions. It was expected that the MA group would show higher PFC activity, larger COP excursions, and poorer performance during DT than the YA group. PFC activity was larger during DT and during the fixed condition but did not differ between groups. COP excursion was also greater when attention was 'fixed' and was consistently larger in MA. MA drove a positive correlation between PFC activity and COP excursion during DT indicative of a higher attentional demand during distraction. Taken together, this study suggests that PFC processing and posture control are different in middle aged adults compared to young adults.