  The objective of the present work is to measure postural kinematics and power
spectral variation from HD-EEG to assess changes in cortical activity during
adaptation and habituation to postural perturbation. To evoke proprioceptive
postural perturbation, vibratory stimulation at 85 Hz was applied to the calf
muscles of 33 subjects over four 75-second stimulation periods. Stimulation was
performed according to a pseudorandom binary sequence. Vibratory impulses were
synchronized to high-density electroencephalography (HD-EEG, 256 channels).
Changes in absolute spectral power (ASP) were analyzed over four frequency
bands (Delta: 0.5-3.5 Hz; theta: 3.5-7.5 Hz; alpha: 7.5-12.5 Hz; beta:12.5-30
Hz). A force platform recorded torque actuated by the feet, and normalized sway
path length (SPL) was computed as a construct for postural performance during
each period. SPL values indicated improvement in postural performance over the
trial periods. Significant variation in absolute power values (ASP) was found
in assessing postural adaptation: an increase in theta band ASP in the
frontal-central region for closed-eyes trials, an increase in theta and beta
band ASP in the parietal region for open-eyes trials. In habituation, no
significant variations in ASP were observed during closed-eyes trials, whereas
an increase in theta, alpha, and beta band ASP was observed with open eyes.
Furthermore, open-eyed trials generally yielded a greater number of significant
ASP differences across all bands during both adaptation and habituation,
suggesting that following cortical activity during postural perturbation may be
up-regulated with the availability of visual feedback. Results provide deeper
insight into pathological postural control failure by exploring the dynamic
changes in both cortical activity and postural kinematics during adaptation and
habituation to proprioceptive postural perturbation.
