Modulation of cortical activity in response to visually induced postural perturbation: combined VR and EEG study

Abstract

There is evidence from EEG studies that unexpected perturbations to standing posture induce a differential modulation of cortical activity compared to self-initiated and/or predictable conditions. However, the neural correlates of whole body postural response to visually induced perturbations on standing posture have not been examined. Here we employ a novel experimental paradigm via combined virtual reality (VR) and EEG measures to examine the effects of visually induced perturbations on the dynamics of postural responses. Twelve Penn State student-athletes without prior history of neurologic disorders and/or orthopaedic injuries participated in this study. There were no differences in response/reaction time measures between both spatially and temporally unpredictable and fully predictable conditions (p>.05). However, significantly stronger modulation of frontal-central EEG theta activity was present prior to onset of unpredictable postural perturbations (p<.05). It is postulated that enhanced EEG theta in unpredictable conditions reflects increased effort to recruit additional brain resources to meet the demands of the postural tasks.

Figure 1

(a) visual stimulus via realistically Virtual “moving room” enable to shift optic flow from Anterior-posterior to Medial-Lateral directions; (b) Time serious of moving room oscillation (.2 Hz) superimposed on a subject’s responses via head motion tracking; (c) wavelet transform depicting the dynamics of head motion/virtual room oscillation and response to visual perturbation. Where: X-axis is time of trial duration (30s); y-axis is the frequency of moving room and the subject’s head oscillation (.2 Hz); Color scale indicates the magnitude of moving room/head motion coherence within .2 Hz frequency cluster.

Figure 2

2D plots of EEG theta power prior to predictable and unpredictable perturbations. It should be noted that reduction of central theta power after the pulse in unpredictable condition was accompanied by significant increase of theta power in frontal and temporal-parietal ROIs. This interesting finding requires additional experimentation and beyond the scope of this report.