Visual Effect on Brain Connectome That Scales Feedforward and Feedback Processes of Aged Postural System During Unstable Stance

Abstract

Older adults with degenerative declines in sensory systems depend strongly on visual input for postural control. By connecting advanced neural imaging and a postural control model, this study investigated the visual effect on the brain functional network that regulates feedback and feedforward processes of the postural system in older adults under somatosensory perturbations. Thirty-six older adults conducted bilateral stance on a foam surface in the eyes-open (EO) and eyes-closed (EC) conditions while their center of pressure (COP) and scalp EEG were recorded. The stochastic COP trajectory was modeled with non-linear stabilogram diffusion analysis (SDA) to characterize shifts in postural control in a continuum of feedback and feedforward processes. The EEG network was analyzed with the phase-lag index (PLI) and minimum spanning tree (MST). The results indicated that visual input rebalanced feedforward and feedback processes for postural sway, resulting in a greater critical point of displacement (CD), short-term effective diffusion coefficients (Ds) and short-term exponent (Hs), but the smaller critical point of time (CT) and long-term exponent (Hl) for the EC state. The EC network demonstrated stronger frontoparietal-occipital connectivity but weaker fronto-tempo-motor connectivity of the theta (4–7 Hz), alpha (8–12 Hz), and beta (13–35 Hz) bands than did the EO network. MST analysis revealed generally greater leaf fraction and maximal betweenness centrality (BCmax) and kappa of the EC network, as compared with those of the EO network. In contrast, the EC network exhibited a smaller diameter and average eccentricity than those of the EO network. The modulation of long-term negative feedback gain of the aged postural system with visual occlusion was positively correlated with leaf fraction, BCmax, and kappa, but negatively correlated with the diameter and average eccentricity for all EEG sub-bands. In conclusion, the aged brain functional network in older adults is tuned to visual information for modulating long-term negative feedback of the postural system under somatosensory perturbations.

Adaptations of postural sway dynamics and cortical response to unstable stance with stroboscopic vision in older adults

“…The hypothesis of intermittent motor control ( Miall et al, 1993 ) posited that postural fluctuations stem from superimposition of centrally-scaled pulse elements to tune postural responses that deviate from the target goal. Central to this interpretation is that the older adults with SV reduced the number of corrective attempts (or reduced the frequency of motor explorations) for postural corrections ( Paillard and Noe, 2015 ; Tsai et al, 2018 ; Chen et al, 2021b ). According to the minimum entropy principle ( Hur et al, 2019 ), postural fluctuations of lower entropy are less automatic due to more volitional efforts being invested in postural control ( Borg and Laxaback, 2010 ; Roerdink et al, 2011 ).…”

“…Tuned to visual availability, alpha power (8–12 Hz) activity is the most prominent feature in the posterior brain ( Mierau et al, 2017 ; Chen et al, 2021b ). According to the cortical idling hypothesis, increases in alpha activity over the sensorimotor area are related to sluggish execution of movements ( Pfurtscheller et al, 1996 ).…”

“…Compared to young adults, the elderly show lower increases in alpha activity without significant potentiation of the high-frequency beta wave when standing with their eyes closed ( Lin et al, 2021 ). Also, eye closure leads to stronger frontoparietal-occipital connectivity but weaker fronto-tempo-motor connectivity of the theta, alpha, and beta bands in older adults ( Chen et al, 2021b ). These findings highlight the fact that brain activation in older adults during bipedal stance is reorganized in response to complete visual occlusion ( Chen et al, 2021b ; Lin et al, 2021 ).…”

“…Also, eye closure leads to stronger frontoparietal-occipital connectivity but weaker fronto-tempo-motor connectivity of the theta, alpha, and beta bands in older adults ( Chen et al, 2021b ). These findings highlight the fact that brain activation in older adults during bipedal stance is reorganized in response to complete visual occlusion ( Chen et al, 2021b ; Lin et al, 2021 ). In fact, older adults are less capable of redistributing the relative sensory weighting to non-visual channels for postural control, as those non-visual sensory systems are more susceptible to degenerative changes ( Bugnariu and Fung, 2007 ; Franz et al, 2015 ).…”

“…In addition to regional activities in the sensorimotor and visual cortex, posture control involves in coordinated processing of cortical activities within these spatially distinct areas, especially when the effect of visual cues is manipulated ( Chen et al, 2021a ; 2021b , 2022 ). By examining COP dynamics, regional/inter-regional EEG features, and COP-EEG interaction, this study investigated neuromechanical control of upright balance with stroboscopic vision for older people, while they were standing on a stabilometer surface with visual feedback.…”