Changes in the activity of the cerebral cortex relate to postural response modification when warned of a perturbation

Abstract

Objective-To determine whether the cerebral cortex contributes to modifying upcoming postural responses to external perturbations when provided with prior warning of the perturbation.Methods-Electroencephalographic (EEG) potentials were recorded from 12 healthy human subjects (21-32 years of age) before perturbing their balance with backward translations of a platform under their feet. The subjects responded with and without a visual cue that warned them 2 seconds before the perturbation (the Cue and No Cue conditions, respectively).Results-Contingent negative variation (CNV) was evident before perturbation onset in only the Cue condition. In the Cue condition, the subjects also produced smaller center of pressure (CoP) displacements than in the No Cue condition. The cue-related difference in the subjects' CNV potentials correlated with the cue-related difference in their CoP displacements. No significant associations existed among the CNV potentials and any cue-related postural adjustments made before the perturbation.Conclusions-Cortical activity before an externally triggered perturbation associates with modifications of the ensuing postural response.Significance-This is the first study to demonstrate a cortical correlate for changes in central postural set that modify externally triggered postural responses based on anticipation.

Preparatory cortical and spinal settings to counteract anticipated and non-anticipated perturbations

“…Changes in cortical activation assessed by electroencephalogram (EEG) prior to a perturbation indicate that the preparatory setting is -at least partly -cortically mediated. This is evidenced by EEG responses depending on pre-cues about the occurrence of a perturbation (Jacobs et al, 2008) as well as by higher preparatory cortical EEG-signals in non-anticipated compared to anticipated perturbations (Mochizuki et al, 2010).…”

Startle induces early initiation of classically conditioned postural responses

“…However, the current work has introduced an alternative explanation to the previously observed effects of cues on PRs. Previously, experimenters have utilized cued perturbations and noted changes compared with unexpected perturbations in EMG onset latencies and amplitudes or COP excursions that were later attributed to central set (Jacobs et al 2008) or attention (Müller et al 2004(Müller et al , 2007 effects. Alternatively, our findings suggest that introducing cues to postural tasks may cause changes to PR characteristics through mechanisms related to classical conditioning or motor preparation.…”

“…Readiness potentials observed in cortical activity that normally precedes the onset of cued or self-initiated postural perturbations support at least some level of preparation before initiating reactive PRs (Adkin et al 2008;Jacobs et al 2008;Mochizuki et al 2010). Further evidence of PR motor preparation has emerged from studies that used cued balance perturbations in classical conditioning paradigms.…”

The effects of predictability on inter-limb postural synchronization prior to bouts of postural instability

“…These examples illustrate the capacity of the CNS to modulate gain in accordance with task demands by coupling or decoupling between-limb coordination as necessary given current contextual requirements or previous experience (i.e. depending on whether the conditions under which postural instability is experienced are known or familiar) [15]. The extent of inter-limb synchronization of COP displacements reflects the coordination of muscle activation patterns between limbs [16] and is a sensitive measure of balance control [17][18][19].…”