Interference to consolidation phase gains in learning a novel movement sequence by handwriting: dependence on laterality and the level of experience with the written sequence.

Practice on a novel sequence of movements can lead to two behavioral expressions of procedural memory consolidation processes: delayed performance gains evolving hours after the termination of training, but also a decrease in the susceptibility of the training-related gains to interference by subsequent experience within a few hours following training. It is not clear what types of experience constitute effective interference for a given task. We recently showed that the handwriting of words in a well-practiced script immediately after training on the finger opposition sequence (FOS) learning task interfered with the expected delayed gains. Here, in Experiment 1, we compared the degree of interference, on FOS learning with the left or the right hand, exerted by writing common words using the right, dominant, hand. Robust interference occurred only when practice in the FOS and the subsequent handwriting were performed with the same hand. In Experiment 2 we tested whether the level of experience with the writing sequence affected the degree of interference on FOS learning. As opposed to writing common words, there was no interference to the FOS gains by writing non-words, composed of the same letters as the common words, even when both tasks were executed with the same hand. Given that interference occurs when there is a critical overlap between the neuronal representations of two tasks, our results indicate that the extent of overlap between the representations is related, at least in part, to motor lateralization and to the level of experience with the interfering task.