Abstract
Increase in postural-demand resources does not necessarily degrade a concurrent motor task, according to the adaptive resource-sharing hypothesis of postural-suprapostural dual-tasking. This study investigated how brain networks are organized to optimize a suprapostural motor task when the postural load increases and shifts postural control into a less automatic process. Fourteen volunteers executed a designated force-matching task from a level surface (a relative automatic process in posture) and from a stabilometer board while maintaining balance at a target angle (a relatively controlled process in posture). Task performance of the postural and suprapostural tasks, synchronization likelihood (SL) of scalp EEG, and graph-theoretical metrics were assessed. Behavioral results showed that the accuracy and reaction time of force-matching from a stabilometer board were not affected, despite a significant increase in postural sway. However, force-matching in the stabilometer condition showed greater local and global efficiencies of the brain networks than force-matching in the level-surface condition. Force-matching from a stabilometer board was also associated with greater frontal cluster coefficients, greater mean SL of the frontal and sensorimotor areas, and smaller mean SL of the parietal-occipital cortex than force-matching from a level surface. The contrast of supra-threshold links in the upper alpha and beta bands between the two stance conditions validated load-induced facilitation of inter-regional connections between the frontal and sensorimotor areas, but that contrast also indicated connection suppression between the right frontal-temporal and the parietal-occipital areas for the stabilometer stance condition. In conclusion, an increase in stance difficulty alters the neurocognitive processes in executing a postural-suprapostural task. Suprapostural performance is not degraded by increase in postural load, due to (1) increased effectiveness of information transfer, (2) an anterior shift of processing resources toward frontal executive function, and (3) cortical dissociation of control hubs in the parietal-occipital cortex for neural economy.
Highlights
Postural control is a continuum raging from “controlled to automatic” processing, depending on the level of postural demand and the capacity of attentional resources (Stins et al, 2009; Boisgontier et al, 2013)
The paired t-test revealed that the force-matching error (NFE: level-surface = 9.89 ± 0.78%; stabilometer = 10.01 ± 0.79%) and reaction time (RT: levelsurface = 304.8 ± 9.6 ms; stabilometer = 310.7 ± 9.8 ms) of the force-matching task did not change with stance configuration (p > 0.05; Table 1)
In terms of synchronization likelihood, we found significant stance effects on inter-regional coupling of ERP in the preparatory stage
Summary
Postural control is a continuum raging from “controlled to automatic” processing, depending on the level of postural demand and the capacity of attentional resources (Stins et al, 2009; Boisgontier et al, 2013). Postural sway is less regular in the dual-task condition than in a single postural task (Donker et al, 2007; Kuczynski et al, 2011) In this context, at least two critical issues with the limited central resource arise. The reason is that the task quality of a suprapostural motor task must take kinematical advantages of stance stability (Wulf et al, 2004; Stoffregen et al, 2007; Huang and Hwang, 2013), whereas a postural-suprapostural task with a cognitive goal typically has low response compatibility between the two component tasks (Weeks et al, 2003)
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