Perturbation-evoked electrodermal activity responds to instability, not just motor or sensory drives

To determine whether electrodermal responses (EDRs) evoked by postural perturbations were sensitive to the context of compensatory balance control, or simply reflected sensory or motor components of the reaction.

Thirteen participants were perturbed backwards in an upright chair and (1) performed compensatory reach-to-grasp movements to a handhold to recover balance (COMP); (2) received the perturbation only and the chair stopped via mechanical support (SENS); and (3) performed rapid self-initiated reach-to-grasp movements without perturbation (MOT).

EDRs were most frequent and largest in the COMP task, observed in 100% of trials (1.42+/-0.16 microS), compared to 39% of SENS trials (0.31+/-0.12 microS, p<0.0001) and 85% of MOT trials (0.98+/-0.25 microS, p=0.073). EDRs in the MOT task followed two patterns across individuals, leading to post-hoc division of subjects into groups (smaller EDRs than COMP task, n=7, versus equivalent EDRs to COMP task, n=6). Motor patterns were equivalent in both groups, indicating that EDRs did not co vary with efferent drive.

Perturbation-evoked EDRs are not a direct reflection of sensory input or motor drive.

These findings suggest that evoked autonomic activity may play a functional role in compensatory postural control.