Involvement of the autonomic nervous system in motor adaptation: acceleration or error reduction?

In the last few decades motor adaptation was extensively studied observing the invariant features of reaching movements. In a parallel neurobehavioral line of research emotional learning was studied under the umbrella of the 'two-factor theory of learning'. In this study we explore the relation between motor learning and the autonomic response (heart rate, HR) of subjects performing point to point reaching movements holding a computer mouse. We consider two alternative outcomes: one is that autonomic response correlates with the learning rate and the second is that the autonomic response correlates with the residual error at the steady state. Eighteen subjects performed reaching movements under perturbed visual feedback demonstrating learning and after effects of learning. The hand movement as well as an Electrocardiogram signal were recorded throughout the training and carefully analyzed offline to extract the trial by trial error as well as the heart period. The results show clear correlation between the change in HR and the residual error but no correlation between the change in HR and the learning rate supporting the second alternative that the sensitivity to errors but not the learning rate correlates with the autonomic response. A control group of another seven subjects underwent the same experiment without the perturbed visual feedback. This control group showed no change in the HR. Further studies are required to validate this hypothesis and unravel the mechanism by which the autonomic response correlates with the residual motor error.