Contribution of cognitive functions to postural control in anticipating self-paced and externally-triggered lower-limb perturbations

Assessing motor competence in kicking in individuals with Down syndrome through wearable motion sensors

BACKGROUND

Kicking a ball is a very frequent action in sport and leisure time activities and a low proficiency in this skill could limit the participation in recreational sport activities. This issue is emphasised in individuals with Down syndrome (IDS) for which data about motor competence in kicking are limited to children. Here, we aim at evaluating the kicking competence of IDS combining a qualitative and a quantitative method.

METHODS

Twenty-three adult IDS and 21 typically developed individuals (ITD) volunteered to participate in the study. Peak-to-peak 3D linear acceleration and angular velocity were recorded at 200 samples/s using two inertial measurement units placed on the lower back and lateral malleolus of the dominant limb during kicking. Motor competence in kicking was assessed according to the criteria proposed in the test of gross motor development version 3 (TGMD-3).

RESULTS

Individuals with Down syndrome showed lower motor competence (ITD: 5.9 ± 1.2; IDS: 3.2 ± 2.0) and lower angular velocities about the cranio-caudal (ITD: 3.0 ± 1.8; IDS: 2.1 ± 1.1 rad/s) and medio-lateral axes (ITD: 4.5 ± 1.5; IDS: 3.0 ± 1.1 rad/s) of the trunk compared with ITD. Shank angular velocity about the medio-lateral axis was lower in IDS (ITD: 14.3.6 ± 4.0; IDS: 9.9 ± 2.8 rad/s).

CONCLUSIONS

The lower trunk angular velocity in IDS may limit the possibility to rely on the proximal-to-distal sequencing commonly observed in kicking and generate high shank angular velocity upon ball impact. The lower trunk angular velocity may result from orthopaedic features of the pelvic girdle and possibly from a poorer neuromuscular control of core muscles.

Assessment of Biomechanical Predictors of Occurrence of Low-Amplitude N1 Potentials Evoked by Naturally Occurring Postural Instabilities

Naturally occurring postural instabilities that occur while standing and walking elicit specific cortical responses in the fronto-central regions (N1 potentials) followed by corrective balance responses to prevent falling. However, no framework could simultaneously track different biomechanical parameters preceding N1s, predict N1s, and assess their predictive power. Here, we propose a framework and show its utility by examining cortical activity (through electroencephalography [EEG]), ground reaction forces, and head acceleration in the anterior-posterior (AP) direction. Ten healthy young adults carried out a balance task of standing on a support surface with or without sway referencing in the AP direction, amplifying, or dampening natural body sway. Using independent components from the fronto-central cortical region obtained from subject-specific head models, we first robustly validated a prior approach on identifying low-amplitude N1 potentials before early signs of balance corrections. Then, a machine learning algorithm was used to evaluate different biomechanical parameters obtained before N1 potentials, to predict the occurrence of N1s. When different biomechanical parameters were directly compared, the time to boundary (TTB) was found to be the best predictor of the occurrence of upcoming low-amplitude N1 potentials during a balance task. Based on these findings, we confirm that the spatio-temporal characteristics of the center of pressure (COP) might serve as an essential parameter that can facilitate the early detection of postural instability in a balance task. Extending our framework to identify such biomarkers in dynamic situations like walking might improve the implementation of corrective balance responses through brain-machine-interfaces to reduce falls in the elderly.

Visuomotor control dynamics of quiet standing under single and dual task conditions in younger and older adults

Visual input facilitates stable postural control; however, ageing alters visual gaze strategies and visual input processing times. Understanding the complex interaction between visual gaze behaviour and the effects of age may inform future interventions to improve postural control in older adults. The purpose of this study was to determine effects of age and dual task on gaze and postural sway dynamics, and the sway-gaze complexity coupling to explore the coupling between sensory input and motor output. Ten older and 10 younger adults performed single and dual task quiet standing while gaze behaviour and centre of mass motion were recorded. The complexity and stability of postural sway, saccade characteristics, visual input duration and complexity of gaze were calculated in addition to sway-gaze coupling quantified by cross-sample entropy. Dual tasking increased complexity and decreased stability of sway with increased gaze complexity and visual input duration, suggesting greater automaticity of sway with greater exploration of the visual field but with longer visual inputs to maintain postural stability in dual task conditions. In addition, older adults had lower complexity and stability of sway than younger adults indicating less automated and stable postural control. Older adults also demonstrated lower gaze complexity, longer visual input durations and greater sway-gaze coupling. These findings suggest older adults adopted a strategy to increase the capacity for visual information input, whilst exploring less of the visual field than younger adults.

Long-Lasting Event-Related Beta Synchronizations of Electroencephalographic Activity in Response to Support-Surface Perturbations During Upright Stance: A Pilot Study Associating Beta Rebound and Active Monitoring in the Intermittent Postural Control

Movement related beta band cortical oscillations, including beta rebound after execution and/or suppression of movement, have drawn attention in upper extremity motor control literature. However, fewer studies focused on beta band oscillations during postural control in upright stance. In this preliminary study, we examined beta rebound and other components of electroencephalogram (EEG) activity during perturbed upright stance to investigate supraspinal contributions to postural stabilization. Particularly, we aimed to clarify the timing and duration of beta rebound within a non-sustained, but long-lasting postural recovery process that occurs more slowly compared to upper extremities. To this end, EEG signals were acquired from nine healthy young adults in response to a brief support-surface perturbation, together with the center of pressure, the center of mass and electromyogram (EMG) activities of ankle muscles. Event-related potentials (ERPs) and event-related spectral perturbations were computed from EEG data using the perturbation-onset as a triggering event. After short-latency (<0.3 s) ERPs, our results showed a decrease in high-beta band oscillations (event-related desynchronization), which was followed by a significant increase (event-related synchronization) in the same band, as well as a decrease in theta band oscillations. Unlike during upper extremity motor tasks, the beta rebound in this case was initiated before the postural recovery was completed, and sustained for as long as 3 s with small EMG responses for the first half period, followed by no excessive EMG activities for the second half period. We speculate that those novel characteristics of beta rebound might be caused by slow postural dynamics along a stable manifold of the unstable saddle-type upright equilibrium of the postural control system without active feedback control, but with active monitoring of the postural state, in the framework of the intermittent control.

Effects of rhythmic visual cues on cognitive resources allocation characterized by electroencephalographic (EEG) features during human gait initiation

Rhythmic visual cues are beneficial in gait initiation (GI) in Parkinson's disease patients with freezing of gait (FOG), however, the underlying neurophysiological mechanism remains poorly understood. The cognitive control modulated by visual cues during GI has been investigated and considered as a potential factor influencing automatic motor actions, but it is unclear how rhythmic visual cues affect cognitive resources demands during GI. The purpose of this study was to explore the effect of rhythmic visual cues on cognitive resources allocation by recording the anticipatory cerebral cortex electroencephalographic (EEG) activity during GI. Twenty healthy participants initiated gait in response to the rhythmic and non-rhythmic visual cues of stimulus presentation. We assessed the contingent negative variation (CNV) of averaged EEG data over 32 electrode positions during GI preparation, the results of which showed that the CNV was induced over prefrontal, frontal, central, and parietal regions in both rhythmic conditions and non-rhythmic conditions. Overall, different visual cues modulated the amplitude of CNV in the early and late stages of the GI preparation. Compared with the non-rhythmic condition, the CNV amplitude was lower in rhythmic condition over displayed regions precede the GI onset. In the late stage of GI preparation, it showed significant differences between the two conditions in prefrontal, frontal, and central regions, and the amplitude of CNV was lower under rhythmic condition. More to the point, the differences were more obvious in the late stage of GI preparation between the two conditions, which was closely associated with the cognitive resources. Therefore, the results indicate that less cognitive resources allocation is required to trigger GI under rhythmic visual cues compared with non-rhythmic visual cues. This study may provide a new insight into why rhythmic visual cues are more effective in improving GI ability compared to non-rhythmic visual cues.

Cerebral preparation of spontaneous movements: An EEG study

OBJECTIVE

The current study sought to determine whether there is a Bereitschaftspotential (BP) before uninstructed, spontaneous movements.

METHODS

14 participants were seated on a comfortable armchair for one hour without any instruction except not to fall asleep and to keep their eyes open. Electroencephalography (EEG) and electromyography (EMG) activity were recorded during the whole session. EEG activity was analyzed before spontaneous movements and compared with EEG activity before repetitive, instructed movements in a separate session.

RESULTS

BPs were identified in most participants with the spontaneous movements. The BPs with spontaneous movements were mostly localized in the medial frontocentral regions. The BPs with the instructed movements were localized primarily in the central regions and had larger amplitude.

CONCLUSION

Presence of a BP before movement does not depend on instruction and may be independent of conscious volition. The amplitude of the BP may depend on the amount of attention.

SIGNIFICANCE

This study shows that the presence of a BP before movement is not an "artifact" of the experimental instructions.