Abstract
Previous studies demonstrated the influence of the post-learning period on procedural motor memory consolidation. In an early period after the acquisition, motor skills are vulnerable to modifications during wakefulness. Indeed, specific interventions such as world-list learning within this early phase of motor memory consolidation seem to enhance motor performance as an indicator for successful consolidation. This finding highlights the idea that manipulations of procedural and declarative memory systems during the early phase of memory consolidation over wakefulness may influence off-line consolidation. Using functional magnetic resonance imaging (fMRI) during initial motor sequence learning and motor sequence recall, we indirectly assess the influence of a secondary task taken place in the early phase of memory consolidation. All participants were scanned using fMRI during the learning phase of a serial reaction time task (SRTT) at 8 a.m. Afterwards, they were randomly assigned to one of five conditions. One group performed a declarative verbal, one a declarative nonverbal learning task. Two groups worked on attention tasks. A control group passed a resting condition. Participants stayed awake the whole day and performed the SRTT in the MRI scanner 12 h later at 8 p.m. At the behavioral level, the analysis of the reaction times failed to show a significant group difference. The primary analysis assessing fMRI data based on the contrast (sequence – random) between learning and retrieval also did not show any significant group differences. Therefore, our main analysis do not support the hypothesis that a secondary task influences the retrieval of the SRTT. In a more liberal fMRI analysis, we compared only the sequence blocks of the SRTT from learning to recall. BOLD signal decreased in the ipsilateral cerebellum and the supplementary motor area solely in the verbal learning group. Although our primary analysis failed to show significant changes between our groups, results of the secondary analysis could be an indication for a beneficial effect of the verbal declarative task in the early post-learning phase. A nonverbal learning task did not affect the activation within the motor network. Further studies are needed to replicate this finding and to assess the usefulness of this manipulation.
Highlights
In 1980, Cohen and Squire postulated a classification of memory systems, describing a declarative and a procedural memory system, including the learning of motor and perceptual contents (Cohen and Squire, 1980)
Our second and more liberal analysis was based on the first level contrast (S2T1 > baselineT1) – (S2T0 > baselineT0) whereby the baseline was the time between two blocks of training and retesting respectively. This resulted in a significant group × time interaction within the left cerebellum (CB) (Figure 3A1) and left supplementary motor area (SMA) (Figure 3B1)
A closer look at this interaction, including all groups, revealed the following: In contrast to the other groups, the verbal learning group (VL) group showed a significant change in BOLD signal in the cerebellum as well as in the supplementary motor area (SMA) comparing the learning to the retesting sessions
Summary
In 1980, Cohen and Squire postulated a classification of memory systems, describing a declarative (learning of facts) and a procedural memory system, including the learning of motor and perceptual contents (Cohen and Squire, 1980). The procedural as well as the declarative aspects of a previously learned content can usually be consolidated distinctly from each other only while asleep because the declarative and procedural memory systems interact during wakefulness but decouples during sleep (Walker et al, 2002; Robertson et al, 2004b; Stickgold, 2005) This interaction during wakefulness was shown by Brown and Robertson: A declarative task can interfere with the process of consolidation of the procedural memory when consolidation takes place over a period of wakefulness but not during sleep (Brown and Robertson, 2007a). This work provided evidence that learning a word list immediately after procedural motor learning in the morning leads to an improvement of motor performance in the evening This effect is lost when consolidation takes place over night. Each active group (verbal learning group and nonverbal learning group) will be separately compared to control groups dealing with verbal material or nonverbal material without a significant memory component
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