Abstract
Acquisition of motor skills often involves the concatenation of single movements into sequences. Along the course of learning, sequential performance becomes progressively faster and smoother, presumably by optimization of both motor planning and motor execution. Following its encoding during training, “how-to” memory undergoes consolidation, reflecting transformations in performance and its neurobiological underpinnings over time. This offline post-training memory process is characterized by two phenomena: reduced sensitivity to interference and the emergence of delayed, typically overnight, gains in performance. Here, using a training protocol that effectively induces motor sequence memory consolidation, we tested temporal and kinematic parameters of performance within (online) and between (offline) sessions, and their sensitivity to retroactive interference. One group learned a given finger-to-thumb opposition sequence (FOS), and showed robust delayed (consolidation) gains in the number of correct sequences performed at 24 h. A second group learned an additional (interference) FOS shortly after the first and did not show delayed gains. Reduction of touch times and inter-movement intervals significantly contributed to the overall offline improvement of performance overnight. However, only the offline inter-movement interval shortening was selectively blocked by the interference experience. Velocity and amplitude, comprising movement time, also significantly changed across the consolidation period but were interference –insensitive. Moreover, they paradoxically canceled out each other. Current results suggest that shifts in the representation of the trained sequence are subserved by multiple processes: from distinct changes in kinematic characteristics of individual finger movements to high-level, temporal reorganization of the movements as a unit. Each of these processes has a distinct time course and a specific susceptibility to retroactive interference. This multiple-component view may bridge the gap in understanding the link between the behavioral changes, which define online and offline learning, and the biological mechanisms that support those changes.
Highlights
Motor Sequence LearningMotor sequence learning refers to the ability to create a link between temporal events, consisting of actions or movements (Adini et al, 2015) and involves transforming a number of discrete movements that are serially executed into a merged representation encompassing multiple anticipated movements, a process known as chunking (Karni, 1996; Gobet et al, 2001; Verwey, 2003; Verwey and Eikelboom, 2003; Sosnik et al, 2004)
In a previous study (Friedman and Korman, 2012), using a keyboard sequence task, we showed that long-term improvements in the number of correct sequences performed were mainly due to reducing intermovement intervals between finger movements
We present the results for the three stages of learning, consolidation and transfer
Summary
Motor Sequence LearningMotor sequence learning refers to the ability to create a link between temporal events, consisting of actions or movements (Adini et al, 2015) and involves transforming a number of discrete movements that are serially executed into a merged representation encompassing multiple anticipated movements, a process known as chunking (Karni, 1996; Gobet et al, 2001; Verwey, 2003; Verwey and Eikelboom, 2003; Sosnik et al, 2004). For example, by experiencing a similar but different movement sequence shortly after practicing the first sequence (retroactive interference), the long-term learning of the sequence is hampered (Korman et al, 2003, 2007) Additional factors such as self-guided performance (Friedman and Korman, 2012), structural specificity (Rozanov et al, 2010) and affordance of post-training sleep (Walker et al, 2003; Korman et al, 2007) were shown to affect the resultant long term memory for a given motor sequence
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