Can Electroencephalography (EEG) and Electromyography (EMG) be used to explain the adaptation of the feedforward postural response to repeated continuous postural perturbations

Beard, Caitlin (2024) Can Electroencephalography (EEG) and Electromyography (EMG) be used to explain the adaptation of the feedforward postural response to repeated continuous postural perturbations. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Introduction: A sudden balance perturbation is often accompanied by postural instability which can be causal to falls. However, repeated exposure to such balance perturbations is characterised by improved balance control, through adaptation of the reactive and/or feedforward postural responses. The oscillating platform paradigm provides an interesting and meaningful experimental approach that elicits both reactive and anticipatory responses when exposed to a few sinusoidal cycles within a trial-by trial basis. The N1 cortical response has been investigated as a function to different biomechanical characteristics of perturbations, however, research is limited regarding the N1 modulation and its contribution to the maintenance and adaptation of postural responses. Aims: The aim of this thesis was to investigate how feedforward postural responses indicate adaptation to repeated continuous transient balance perturbations, through postural muscle organisation and changes in the N1 potentials relative to the onset of the perturbation and changes of frequency. Hypothesis: It was hypothesised that postural adaptation would be manifested over numerous repeated trials, evidenced by reduced muscular activation relative to platform direction (anteroposterior), changes in centre of pressure metrics (reduced peak velocity), and a reduction in initial N1 potentials and amplitudes which reflects a decrease in cognitive workload over trials. Methods: Twenty-one healthy young adults (12 males, 9 females; mean  SD = 27  4.83 years) participated in this study. Each participant was instrumented EMG electrodes (2000 Hz) on the GM and TA muscles on both legs. Participants were fitted with a 32-channel EEG cap (1000 Hz). Participants were stood on the oscillating platform barefoot and shoulder-width apart moving in an anteroposterior direction at 0.25 Hz for 10 cycles and 0.5 Hz for 15 cycles per trial (each trial lasting 95 seconds to 1-minute). Force plates embedded into the platform recorded ground reaction forces (1000 Hz) in which all relevant centre of pressure metrics were obtained. Postural adaptation was measured over the 10 repeating trials. Statistical analyses were performed using repeated measured (ANOVA) via SPSS statistics with within-subject factor of trial (T1-T10). Polynomial trend analyses found significant effects and post-hoc analyses were performed using pairwise comparisons. Results: The N1 amplitude and EMG activity of both the TA and GM showed significant adaptation over the 10 trials with both of them dramatically reducing in terms of the onset of the perturbation and change of frequency, this was also the case for COP dynamics which began with a large acceleration in both anteroposterior directions which reduced over time. Discussion: This study demonstrated a significant interaction between the cortical N1 potential, muscular activation, and COP dynamics during postural equilibrium, providing further insight into neural control of balance. Both N1 amplitude and muscular activation reduced over time indicating the collaborative work of the neuro-muscular system in terms of balance control. COP adjustments in the backwards direction were significantly faster than in the forwards direction which indicates directional response properties of the balance control system. The results emphasise the efficiency of neuro-muscular coordination relative to repeated exposure to continuous perturbations, which is characteristic of adaptive processes occurring within the response strategies. Future research should be directed at investigating such responses in other populations (e.g. ageing and neurodegenerative disorders) and rehabilitative strategies that focus on adaptive postural control.