Frequency characteristics of cortical activity associated with perturbations to upright stability.

Cortical evoked potentials are evident in the control of whole-body balance reactions in response to transient instability. The focus of this work is to continue to advance understanding of the potential cortical contributions to bipedal balance control. Temporally unpredictable postural perturbations evoke a negative potential (N1), which has drawn parallels to error-related negativity (ERN) as well as visual and auditory evoked N1 responses. The mechanism underlying the generation of event-related potentials (ERPs) has been a matter of debate for the past few decades. While the evoked model proposes that ERPs are generated by the addition of fixed latency and fixed polarity responses, the phase reorganization model suggests that ERPs are the result of stimulus-induced phase reorganization of the ongoing oscillations. Previous studies have suggested phase reorganization as a possible mechanism in auditory N1, visual N1 and error-related negativity (ERN). The purpose of the current study was to explore the frequency characteristics of the cortical responses to whole-body balance perturbations. Perturbations were evoked using a lean and release protocol. The results revealed a significant power increase and phase-locking of delta, theta, alpha, and beta band activity during perturbation-evoked N1. This may suggest that the stimulus-induced phase reorganization of the ongoing electroencephalographic (EEG) activity could account for the features of cortical ERPs in response to perturbation of upright stability.