Off-line learning of motor skill memory: a double dissociation of goal and movement.

Acquiring a new skill requires learning multiple aspects of a task simultaneously. For example, learning a piano sonata requires learning the musical notes and being able to implement this goal by learning the appropriate sequence of finger movements. After practice, skill continues to develop off-line during a period of consolidation. Here we show that different aspects of a procedural memory are processed separately during consolidation: Only the movement sequence is enhanced over the day; whereas only the goal is enhanced over a night of sleep. This double dissociation suggests that distinct systems, enhancing different aspects of a procedural memory, support improvements during consolidation. Consolidation is not a single process; instead, there are multiple routes to off-line learning, and the engagement of these distinct mechanisms is determined by when consolidation takes place.