Examining interference of different cognitive tasks on voluntary balance control in aging and stroke.

This study compared the effect of semantic and working memory tasks when each was concurrently performed with a voluntary balance task to evaluate the differences in the resulting cognitive-motor interference (CMI) between healthy aging and aging with stroke. Older stroke survivors (n = 10), older healthy (n = 10) and young adults (n = 10) performed the limits of stability, balance test under single task (ST) and dual task (DT) with two different cognitive tasks, word list generation (WLG) and counting backwards (CB). Cognitive ability was evaluated by recording the number of words and digits counted while sitting (ST) and during balance tasks (DT). The balance and cognitive costs were computed using [(ST-DT)/ST] × 100 for all the variables. Across groups, the balance cost was significantly higher for the older stroke survivors group in the CB condition than older healthy (p < 0.05) and young adult groups (p < 0.05) but was similar between these two groups for the WLG task. Similarly, the cognitive cost was significantly higher in older stroke survivors than in older healthy (p < 0.05) and young adults (p < 0.01) for both the cognitive tasks. The working memory task resulted in greater CMI than the semantic one, and this difference seemed to be most apparent in older stroke survivors. Young adults showed the least CMI, with a similar performance on the two memory tasks. On the other hand, healthy aging and stroke impact both semantic and working memory. Stroke-related cognitive deficits may further significantly decrease working memory function.