Sleep saves the effector independent representation of a motor skill

During off-line memory consolidation a motor skill is less vulnerable to interference (stabilisation) and significantly enhances in performance (enhancement). In the present study we test the hypothesis if off-line consolidation of motor memories contributes in the process of generalisation in the motor domain. Participants learned with their left hand a sequential finger tapping task sensitive for motor skill learning. Generalisation was tested by the ability to transfer the original sequence (extrinsic transformation) or the mirror sequence (intrinsic transformation) to the right hand in contrast to a new sequence that was not learned before. To assess the acute effects on generalisation, transfer was assessed immediately after training of the left hand. To study the effects of off-line consolidation participants were tested after an interval of daytime (training at 8am and testing retrieval of the transfer sequences at 8pm) or after an interval of night time including sleep (training at 8pm and testing for retrieval of the transfer sequences at 8am). Shortly after training of the left hand significant transfer effects were evident for extrinsic transformed sequences of the right hand but there was no advantage for the intrinsic transferred sequences compared with a new sequence. After a period of daytime being awake the advantage of the transfer from the left hand to the right hand on extrinsic formed sequences had vanished and intrinsic transformed sequences were not transferred anymore. A period of night time that included sleep saves the initial transfer effect for extrinsic transformed sequences without an effect on the intrinsic transformed movements. These results show that an effector-independent representation of a skill is evident soon after the initial training and sleep has the capacity to save this transfer in the motor system. These results give evidence that sleep participate in the process of generalisation of a motor skill.