Cortical recruitment and functional dynamics in postural control adaptation and habituation during vibratory proprioceptive stimulation

Abstract

Objective. Maintaining upright posture is a complex task governed by the integration of afferent sensorimotor and visual information with compensatory neuromuscular reactions. The objective of the present work was to characterize the visual dependency and functional dynamics of cortical activation during postural control.Approach. Proprioceptic vibratory stimulation of calf muscles at 85 Hz was performed to evoke postural perturbation in open-eye (OE) and closed-eye (CE) experimental trials, with pseudorandom binary stimulation phases divided into four segments of 16 stimuli. 64-channel EEG was recorded at 512 Hz, with perturbation epochs defined using bipolar electrodes placed proximal to each vibrator. Power spectra variation and linearity analysis was performed via fast Fourier transformation into six frequency bands (Δ, θ, α, β, γ_low, and γ_high,. Finally, functional connectivity assessment was explored via network segregation and integration analyses.Main Results. Spectra variation showed waveform and vision-dependent activation within cortical regions specific to both postural adaptation and habituation. Generalized spectral variation yielded significant shifts from low to high frequencies in CE adaptation trials, with overall activity suppressed in habituation; OE trials showed the opposite phenomenon, with both adaptation and habituation yielding increases in spectral power. Finally, our analysis of functional dynamics reveals novel cortical networks implicated in postural control using EEG source-space brain networks. In particular, our reported significant increase in local θ connectivity may signify the planning of corrective steps and/or the analysis of falling consequences, while α band network integration results reflect an inhibition of error detection within the cingulate cortex, likely due to habituation.Significance. Our findings principally suggest that specific cortical waveforms are dependent upon the availability of visual feedback, and we furthermore present the first evidence that local and global brain networks undergo characteristic modification during postural control.

Postural Control Adaptation and Habituation During Vibratory Proprioceptive Stimulation: An HD-EEG Investigation of Cortical Recruitment and Kinematics

“…There are two main limitations to note from this methodology. Firstly, while it remains possible that the onset of habituation or fatigue may differ subject-to-subject, previous studies have shown that ant-post and lat torque variations during OE and CE trials reach a consistent minimum around 150-200 seconds following incident stimuli, corresponding with P3 in the present work [3], [10]. Nevertheless, further investigation into quantitative indicators for the measurement of cortical habituation is recommended.…”

“…Postural sway was recorded to obtain normalized SPL values over five experimental periods, which were then utilized to classify postural adaptation and postural habituation as differences in ASP between specific recording periods. In this regard, adaptation was defined as the difference between P1 and QS periods, in accordance with extant postural perturbation literature [3], [10], [12]. However, normalized SPL was used to define postural habituation, where P1 ASP values were subtracted from the period with the lowest mean SPL to avoid the influence of time-dependent variations such as fatigue.…”

“…When describing time-varying phenomena, a distinction must be made between true adaptation resulting from control dynamic alterations and other time-dependent phenomena, such as fatigue or biomechanical alterations resultant from changes in balance conditions [3]. Because of this, we aimed to use SPL results to observe whether postural performance decreased over any of the experimental periods; with both OE and CE conditions, minimum postural sway has been reported to occur at around 150-200 seconds following incident stimuli [3], [10]. Table I shows the means and standard deviations of the normalized SPL values for the present cohort, across each of the experimental periods and conditions.…”

“…While recent evidence for the critical role of the cerebral cortex in governing postural adaptation and habituation has been reported [10], to our knowledge, cortical activity assessment during balance perturbation has never been synchronized with kinematic posturography measurements. In addition, no postural control studies report the use of 'highdensity', 256-channel EEG (HD-EEG)a methodology with superior spatial resolution to more conventional 32-or 64channel systems.…”

“…Exogenous disruption or nonspecific stimulation of these systems can induce postural sway [5], [6] the magnitude and latency of which characterize the kinematics of postural control, which can be assessed by changes in force and torque actuated at the support surface of the feet, altogether known as posturography [7], [8], [9]. Postural control measurement is often employed under conditional balance perturbation, which is typically achieved via visual disturbance or proprioceptive stimulation [10]. Extant research in this regard cites postural control as a fundamental 'learned' motor skill, whose function and efficiency can be systematically improved with routine postural tasks [9] or directed training [11].…”