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Publication

Motor Memory Formation: A Neurobehavioral Investigation

Book - Dissertation

Memory formation covers unique and divergent stages. After performing a new action, encoding takes place and forms a representation of this action in the brain. The novel memory trace is then stabilized through subsequent stages of a time dependent process referred to as memory consolidation. Consolidation makes the memory more resistant against competing influences, interference or forgetting in the absence of further practice and allows retention and retrieval in the future. However, upon recall the memory becomes modifiable again since reactivation of a stable memory destabilizes the memory representation. In order to persist over longer time-periods, these reactivated memories require re-stabilization; i.e. a process called reconsolidation. The aim of this doctoral project was to investigate the dynamics of motor memory formation with a specific focus on the three fundamental underlying processes: encoding, consolidation, and recall. In the first part of this doctoral project, we investigated the role of sleep in maintaining the capacity for motor memory encoding. The study rationale was based on the synaptic homeostasis hypothesis which suggests that the evident homeostatic regulation of sleep and sleep need is linked to mechanisms of plasticity and learning capabilities of the brain. We reported, in line with the synaptic homeostasis hypothesis, that baseline corticomotor excitability increased after a 12h-period awake and that the brain’s capacity to exhibit motor learning-induced plasticity was reduced by the end of the day. We show that especially slow wave sleep is necessary to renormalize the daily increase in synaptic strength due to spontaneous synaptic plasticity when awake and restore the brain’s capacity to encode new memories. In the second part, we focused on the role of movement observation in motor memory consolidation. We reported that observing the same type of movement as previously practiced (congruent movement stimuli) substantially improved performance on a retention test shortly after training in comparison to observing either an incongruent movement type or control stimuli. On the other hand, no differences in retention were found when either observation followed 24h after initial training. In summary, we showed that once a motor memory is encoded, movement observation is a practical tool to improve early consolidation. In the third part, we investigated the role of reconsolidation upon motor memory recall. We observed that the memory is only fragile for interference during a short time window and further physical practice or even the simple passage of time will re-stabilize the reactivated motor memory. This shows that both length of reactivation and timing of interference constrain whether a memory can be experimentally interfered with and suggests that the role of reconsolidation is to maintain memory relevance for future use. In summary, this doctoral project reflects the complexity of human motor memory formation, and contributes to further the understanding of these fundamental processes for human memory.
Publication year:2015
Accessibility:Open