Generalizability of perturbation-evoked cortical potentials: Independence from sensory, motor and overall postural state.

Following disturbances to postural stability, balance recovery reactions are evoked by numerous sensory inputs and characterized by motor reactions involving different patterns of activity, depending on postural task conditions. It remains unknown whether well-documented cortical responses to instability share common spatio-temporal characteristics, despite variations in the sensory, motor, and postural components of the reactions. The objective was to explore the spatio-temporal profile of cortical potentials evoked by instability requiring either upper- or lower-limb compensatory responses. The hypothesis that upper- and lower-limb balance-correcting reactions are associated with evoked cortical potentials (N1, P2) featuring similar spatio-temporal characteristics was tested by inducing postural perturbations in seated (SIT) or standing (STAND) positions. For both conditions, N1 amplitude was greatest at FCz, with no significant differences in the timing of N1 peak (SIT: 142.4+/-7.95ms; STAND: 148.4+/-4.10ms) or N1 amplitude (SIT: 37.16+/-6.99microV; STAND: 39.08+/-4.51microV). The amplitude of the P2 potential (measured at CPz) was significantly larger in the STAND condition (37.87+/-6.14microV) than in the SIT (23.66+/-6.21microV) condition. Significant differences in P2 peak time between tasks were absent (SIT: 319.9+/-11.45ms; STAND: 322.7+/-7.61ms). Though differences in the amplitude of components of evoked potentials may reflect the extent of cortical involvement in different aspects of postural control, similarities in the spatio-temporal components of cortical potentials between tasks reflects generalizable cortical processing of unexpected stimuli independent of the sensory, motor, or postural aspects of the response.