Abstract
Postural control declines across adult lifespan. Non-physical balance training has been suggested as an alternative to improve postural control in frail/immobilized elderly people. Previous studies showed that this kind of training can improve balance control in young and older adults. However, it is unclear whether the brain of young and older adults is activated differently during mental simulations of balance tasks. For this purpose, soleus (SOL) and tibialis motor evoked potentials (MEPs) and SOL H-reflexes were elicited while 15 elderly (mean ± SD = 71 ± 4.6 years) and 15 young participants (mean ± SD = 27 ± 4.6 years) mentally simulated static and dynamic balance tasks using motor imagery (MI), action observation (AO) or the combination of AO and MI (AO + MI). Young subjects displayed significant modulations of MEPs that depended on the kind of mental simulation and the postural task. Elderly adults also revealed differences between tasks, but not between mental simulation conditions. Furthermore, the elderly displayed larger MEP facilitation during mental simulation (AGE-GROUP; F(1,28) = 5.9; p = 0.02) in the SOL muscle compared to the young and a task-dependent modulation of the tibialis background electromyography (bEMG) activity. H-reflex amplitudes and bEMG in the SOL showed neither task- nor age-dependent modulation. As neither mental simulation nor balance tasks modulated H-reflexes and bEMG in the SOL muscle, despite large variations in the MEP-amplitudes, there seems to be an age-related change in the internal cortical representation of balance tasks. Moreover, the modulation of the tibialis bEMG in the elderly suggests that aging partially affects the ability to inhibit motor output.
Highlights
Postural control is known to decline across adult lifespan
Post hoc analysis showed that the background electromyography (bEMG) was bigger when the elderly imagined the dynamic (p < 0.001) and static balance tasks (p < 0.001) than during the rest condition, compared with the young adults
This means that muscular activity was higher in the elderly than in young subjects at rest and during mental simulation, and differently modulated by the type of balance task (Figure 4)
Summary
Postural control is known to decline across adult lifespan. Non-physical balance training has been suggested as an alternative training for frail people such as older adults. We found that corticospinal excitability was modulated depending on the postural task and the kind of mental simulation performed by young subjects (Mouthon et al, 2015). To date, it is unknown whether the internal mental representation of balance tasks undergoes age-related changes. Analysis of the SOL bEMG activity revealed a main effect of AGE GROUP (F(1,28) = 92.3; p < 0.001) This means that muscular activity was higher in the elderly than in young subjects both at rest and during mental simulation. There was no other main effect or interaction that reached the level of significance
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