Neuroimaging of an attention demanding dual-task during dynamic postural control.

Cognitive tasks impact postural control when performed concurrently as dual-tasks. This is presumed to result from capacity limitations in relevant brain regions. We used functional near-infrared spectroscopy (fNIRS) to measure brain activation of the left motor, temporal, and dorsal-lateral prefrontal brain regions of younger (n=6) and older (n=10) adults. Brain activation was measured during an auditory choice reaction task (CRT) and standing on a dynamic posturography platform, both as single-tasks and concurrently as dual-task. Body sway was assessed by median absolute deviation (MAD) of anterior-posterior translation of the center of mass (COM). Brain activation was measured as changes in oxy-hemoglobin by fNIRS. During both single- and dual-task conditions, we found that older adults had greater brain activation relative to younger adults. During dual task performance, the total activation was less than expected from the sum of individual conditions for both age groups, indicating a dual-task interference (reduction in younger adults=53% [p=0.02]; in older adults=53%; [p=0.008]). This reduction was greater for the activation attributable to the postural task (reduction younger adults=75% [p=0.03]; older adults=59% [p=0.005]) compared to the CRT task (reduction younger adults=10%, [p=0.6]; older adults=7.3%, [p=0.5]) in both age groups. Activation reduction was not accompanied by any significant changes in body sway in either group (older adults: single-task MAD=0.94cm, dual-task MAD=1.10cm, p=0.20; younger adults: single-task RMS=0.95cm, dual-task MAD=1.08cm, p=0.14). Our results indicate that neural resources devoted to postural control are reduced under dual-task conditions that engage attention.