Source monitoring in Alzheimer's Disease

Source monitoring is the process of making judgments about the origin of memories. There are three categories of source monitoring: reality monitoring (discrimination between self- versus other-generated sources), external monitoring (discrimination between several external sources), and internal monitoring (discrimination between two types of self-generated sources). We investigated whether Alzheimer's Disease (AD) patients, when compared with young and older adults, are impaired at the same level on the three source monitoring categories. We designed three tasks, one for each source monitoring category. In the first task, aimed at reality monitoring, participants had to remember whether objects were previously placed in a bag by themselves or by the experimenter. In the second task, assessing external monitoring, participants had to remember whether the experimenter had previously placed objects in the bag with a black or white gloved hand. In the third task, measuring internal monitoring, participants had to remember whether they had previously placed or imagined themselves placing objects in the bag. Participants showed worse performances in the external and internal monitoring tasks, when compared with reality monitoring. The external monitoring deficit was even more pronounced in AD patients. Regression analyses showed that variation in the external monitoring performances was reliably predicted by inhibition. Our results emphasize the role of inhibitory processes in AD patients' source monitoring decline. The close relation between source and inhibitory decline in AD is interpreted in terms of a common neural base for both concepts.     

Learning strategy differentially impacts memory connections in children and adults

Even once children can accurately remember their experiences, they nevertheless struggle to use those memories in flexible new ways—as in when drawing inferences. However, it remains an open question as to whether the developmental differences observed during both memory formation and inference itself represent a fundamental limitation on children's learning mechanisms, or rather their deployment of suboptimal strategy. Here, 7–9-year-old children (N = 154) and young adults (N = 130) first formed strong memories for initial (AB) associations and then engaged in one of three learning strategies as they viewed overlapping (BC) pairs. We found that being told to integrate—combine ABC during learning—both significantly improved children's ability to explicitly relate the indirectly associated A and C items during inference and protected the underlying pair memories from forgetting. However, this finding contrasted with implicit evidence for memory-to-memory connections: Adults and children both formed A-C links prior to any knowledge of an inference test—yet for children, such links were most apparent when they were told to simply encode BC, not integrate. Moreover, the accessibility of such implicit links differed between children and adults, with adults using them to make explicit inferences but children only doing so for well-established direct AB pairs. These results suggest that while a lack of integration strategy may explain a large share of the developmental differences in explicit inference, children and adults nevertheless differ in both the circumstances under which they connect interrelated memories and their ability to later leverage those links to inform flexible behaviours.

Research Highlights

• Children and adults view AB and BC pairs related through a shared item, B. This provides an opportunity for learners to connect A–C in memory.
• Being encouraged to integrate ABC during learning boosted performance on an explicit test of A–C connections (children and adults) and protected from forgetting (children).
• Children and adults differed in when implicit A–C connections were formed—occurring primarily when told to separately encode BC (children) versus integrate (adults), respectively.
• Adults used implicit A–C connections to facilitate explicit judgments, while children did not. Our results suggest developmental differences in the learning conditions promoting memory-to-memory connections.

     

Molecular Mechanisms Associated with the Benefits of Variable Practice in Motor Learning

Abstract

Variable practice promotes a higher level of motor learning than constant practice. The glutamate receptors, n-methyl-d-aspartate (NMDA) and alfa-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA), have been associated with the changes in motor cortex that occur throughout the process of motor learning. Considering that, it is possible that variable practice is more associated with the NMDA and AMPA receptors than constant practice. This study aimed ao investigating the association between the glutamate receptors, NMDA and AMPA, and constant and variable practice schedules. Seventy-eight male mice practiced the rotarod task in a constant or variable scheduling, in two consecutive days (acquisition phase). Learning tests were performed 24?h and 10?days after the end of the acquisition phase. Variable practice was more associated with the NMDA receptor and had a greater AMPA receptor expression than constant practice. The results suggest that the benefits of variable practice are result of both the greater dependency on the NMDA receptor and the greater AMPA receptor expression.