Contribution of cognitive functions to postural control in anticipating self-paced and externally-triggered lower-limb perturbations.
The contribution of higher-order cognitive functions to postural control is poorly understood. It is recognized that the prefrontal cortex (PFC) is active after postural perturbations, however little is known about anticipatory PFC activity occurring before an upcoming perturbation. Here we aim at advancing our understanding on the contribution of higher-order cognitive functions in the fore period before postural perturbations. Thirteen healthy men underwent both self-paced and externally-triggered lower limb perturbations during high-resolution electroencephalography and surface electromyography (sEMG) recordings. Event-related potentials (ERP) and sEMG associated with perturbations were compared between conditions. Both self-paced and externally-triggered perturbations elicited a large prefrontal negativity before the perturbation onset, but the externally-triggered condition evoked larger activity over the left hemisphere; source analysis localized this activity in the PFC. The motor readiness potential occurred earlier and was larger for self-paced perturbations and its origin in premotor areas was confirmed. A larger bilateral activity over lateral occipital derivations was observed for externally-triggered perturbations and was localized in the occipital-temporal cortex, likely within the extrastriate body area (EBA). We confirm that the preparatory activity of premotor areas is associated with the intentional engagement of upcoming actions since it occurs only before self-paced perturbations. The PFC anticipating both perturbations can be interpreted as an unintentional top-down cognitive control required by the tasks, especially involving attention and inhibition. However, before externally-triggered perturbations also other cognitive resources are required. The EBA activity anticipating externally-triggered perturbation may represent a visual prediction of the desired posture.