Dissociating effects of error size, training duration, and amount of adaptation on the ability to retain motor memories

Published Date: 
September 4, 2019

Alhussein L, Hosseini EA, Nguyen KP, Smith MA, Joiner WM

Extensive computational and neurobiological work has focused on how the training schedule, i.e. the duration and rate at which an environmental disturbance is presented, shapes the formation of motor memories. If long-lasting benefits are to be derived from motor training, however, retention of the performance improvements gained during practice is essential. Thus, a better understanding of mechanisms that promote retention could lead to the design of more effective training procedures. The few studies that have investigated how retention depends on the training schedule have suggested that the gradual exposure of a perturbation leads to improved retention of motor memory compared to an abrupt exposure. However, several of these previous studies showed small effects, and while some controlled the training duration and others the level of learning, none have controlled both. Here we disambiguated both of these effects from exposure rate by systematically varying the duration of training, the type of trained dynamics, and exposure rate for these dynamics in human force-field adaptation. After controlling for both training duration and the amount of learning, we found essentially identical retention when comparing gradual and abrupt training for two different types of force-field dynamics. By contrast, we found that retention was markedly higher for long-duration compared to short-duration training for both types of dynamics. These results demonstrate that the duration of training has a far greater effect on the retention of motor memory than the exposure rate during training. We show that a multi-rate learning model provides a computational mechanism for these findings.