Cortical Correlates of Human Balance Control

Abstract

Balance control is a fundamental component of human every day motor activities such as standing or walking, and its impairment is associated with an increased risk of falling. However, in humans the exact neurobiological mechanisms underlying balance control are still unclear. Specifically, although previous studies have identified a number of cortical regions that become significantly activated during real or imagined balancing, the interactions within and between the relevant cortical regions remain to be investigated. The working hypothesis of this study is that cortical networks contribute to an optimization of balance control, and that this contribution can be revealed by partial directed coherence—a time-variant, frequency-selective and directed functional connectivity analysis tool. Electroencephalographic activity was recorded in 37 subjects during single-leg balancing on a stable as well as an unstable surface. Results of this study show that in the transition from balancing on a stable surface to an unstable surface, two topographically delimitable connectivity networks (weighted directed networks) are established; one associated with the alpha and one with the theta frequency band. The theta network sequence can be described as a set of subnetworks (modules) comprising the frontal, central and parietal cortex with individual temporal and spatial developments within and between those modules. In the alpha network, the occipital electrodes O1 and O2 act as a source, and the interactions propagate predominantly in the directions from occipital to parietal and to centro-parietal areas. These important findings indicate that balance control is supported by at least two functional cortical networks.Electronic supplementary materialThe online version of this article (doi:10.1007/s10548-017-0567-x) contains supplementary material, which is available to authorized users.

Tracking the Reorganization of Module Structure in Time-Varying Weighted Brain Functional Connectivity Networks

“…The underlying study investigates the currently only imprecisely understood contribution of the cerebral cortex to compensatory reactions following a sudden balance perturbation in order to regain postural stability. A previous study 21 that focused on time-variant connectivity analysis has explored the same data set and provides a priori information about suitable frequency bands and the dynamics of connectivity changes. The results demonstrate that in the transition from balancing on a stable surface (BSS) to an unstable surface (BUS), two topographically circumscribed, time-varying connectivity networks are established; one is associated with the theta and one with the alpha frequency band.…”

“…21 EEG data from 37 healthy male university students were analyzed. Participants were informed about the experimental protocol and their written consent was obtained beforehand.…”

“…26 For the tvMVAR modeling, the full electrode set consisting of 32 electrodes was used. 21 The connectivity analysis based on the tvMVAR parameters was performed by means of the direct directed transfer function (dDTF).…”

“…grand mean dDTF-TFMs were obtained by averaging over all subjects. A theta frequency sub-band (5-7 Hz) was considered, as EEGactivity in this frequency band is associated with the balance task 21,30 (see also Appendix E). The edge weight w ij (t) of the tth network W t of the resulting time-varying grand mean network W was computed by extracting the median value within the theta frequency sub-band at time t from the corresponding grand mean dDTF-TFM.…”

“…The influence of motion artifacts on the connectivity analysis was investigated in a previous study, 21 whose results can be summarized as follows. It must be considered that the interval ranging from 3 s to 3.5 s is strongly influenced by the BUS onset.…”