A conversion from slow to fast memory in response to passive motion

When the same perturbation is experienced consecutively, learning is accelerated on the second attempt. This savings is a central property of sensorimotor adaptation. Current models suggest that these improvements in learning are due to changes in the brains sensitivity to error. Here, we tested whether these increases in error sensitivity could be facilitated by passive movement experiences. In each experimental group, a robot moved the arm passively in the direction that solved the upcoming rotation, with no visual feedback provided. Following that, participants adapted to a visuomotor rotation. Prior passive movements substantially improved motor learning, increasing total compensation in each group by approximately 30%. Similar to savings, a state-space model suggested that this improvement in learning was due to an increase in error sensitivity, but not memory retention. When we considered the possibility that learning was supported by parallel fast and slow adaptive processes, a striking pattern emerged: whereas initial improvements in learning were driven by a slower adaptive state, increases in error sensitivity gradually transferred to a faster learning system with the passage of time. These findings suggest that passive errors engage motor learning systems, but the resulting behavioral patterns migrate between slow and fast adaptive circuits as the passive memory is consolidated.