Smith MA, Ghazizadeh A, and Shadmehr R (2006) Interacting adaptive processes with multiple timescales underlie short-term motor learning, PLoS Biology 4:e179.

Abstract Multiple processes may contribute to motor skill acquisition, but it is thought that many of these processes require sleep or the passage of long periods of time ranging from several hours to many days or weeks. Here we demonstrate that within a time scale of minutes, two distinct fast-acting processes substantially influence motor adaptation. One process responds weakly to error but retains information well, whereas the other responds strongly but has poor retention. This two-state learning system makes the important prediction of rapid spontaneous recovery (or adaptation rebound) if error feedback is clamped at zero following an adaptation-extinction training episode. We used a novel paradigm to experimentally confirm this prediction in human motor learning of reaching, and we show that the interaction between the learning processes in this simple two-state system provides a unified explanation for several different, apparently unrelated, phenomena in motor adaptation including savings, anterograde interference, and rapid unlearning. This work shows that understanding the interplay between the different processes involved in memory formation can give us fundamental insights into understanding how learning proceeds.