Self-organized reactivation maintains and reinforces memories despite synaptic turnover

Long-term memories are believed to be stored in the synapses of cortical neuronal networks. However, recent experiments report continuous creation and removal of cortical synapses, which raises the question how memories can survive on such a variable substrate. Here, we study the formation and retention of associative memory in a computational model based on Hebbian cell assemblies in the presence of both synaptic and structural plasticity. During rest periods, such as may occur during sleep, the assemblies reactivate spontaneously, reinforcing memories against ongoing synapse removal and replacement. Brief daily reactivations during rest-periods suffice to not only maintain the assemblies, but even strengthen them, and improve pattern completion, consistent with offline memory gains observed experimentally. While the connectivity inside memory representations is strengthened during rest phases, connections in the rest of the network decay and vanish thus reconciling apparently conflicting hypotheses of the influence of sleep on cortical connectivity.

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Reward enhances memory via age-varying online and offline neural mechanisms across development

10.1101/2021.09.14.460286 ◽

2021 ◽

Author(s):

Alexandra O Cohen ◽

Morgan M Glover ◽

Xinxu Shen ◽

Camille V Phaneuf ◽

Kristen N Avallone ◽

...

Keyword(s):

Associative Memory ◽

Neural Circuits ◽

Neural Mechanisms ◽

Age Related ◽

High Reward ◽

Memory Representations ◽

Dopamine Signaling ◽

Reward Motivation ◽

The Brain

Reward motivation enhances memory through interactions between mesolimbic, hippocampal, and cortical systems - both during and after encoding. Developmental changes in these distributed neural circuits may lead to age-related differences in reward-motivated memory and the underlying neural mechanisms. Converging evidence from cross-species studies suggests that subcortical dopamine signaling is increased during adolescence, which may lead to stronger memory representations of rewarding, relative to mundane, events and changes in the contributions of underlying subcortical and cortical brain mechanisms across age. Here, we used fMRI to examine how reward motivation influences the "online" encoding and "offline" post-encoding brain mechanisms that support long-term associative memory from childhood to adulthood. We found that reward motivation led to both age-invariant as well as adolescent-specific enhancements in associative memory after 24 hours. Furthermore, reward-related memory benefits were linked to age-varying neural mechanisms. During encoding, interactions between the prefrontal cortex and ventral tegmental area (VTA) were associated with better high-reward memory to a greater degree with increasing age. Pre- to post-encoding changes in functional connectivity between the anterior hippocampus and VTA were also associated with better high-reward memory, but more so at younger ages. Our findings suggest that there may be developmental shifts - from offline subcortical to online cortical processes - in the brain mechanisms supporting reward-motivated memory.

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Adaptive Repulsion of Long-Term Memory Representations Is Triggered by Event Similarity

Psychological Science ◽

10.1177/0956797620972490 ◽

2021 ◽

pp. 095679762097249

Author(s):

Avi J. H. Chanales ◽

Alexandra G. Tremblay-McGaw ◽

Maxwell L. Drascher ◽

Brice A. Kuhl

Keyword(s):

Associative Memory ◽

Color Space ◽

Long Term Memory ◽

Systematic Bias ◽

Adaptive Memory ◽

Term Memory ◽

Memory Interference ◽

Color Similarity ◽

Memory Representations

We tested whether similarity between events triggers adaptive biases in how those events are remembered. We generated pairs of competing objects that were identical except in color and varied the degree of color similarity for the competing objects. Subjects ( N = 123 across four experiments) repeatedly studied and were tested on associations between each of these objects and corresponding faces. As expected, high color similarity between competing objects created memory interference for object–face associations. Strikingly, high color similarity also resulted in a systematic bias in how the objects themselves were remembered: Competing objects with highly similar colors were remembered as being further apart (in color space) than they actually were. This repulsion of color memories increased with learning and served a clear adaptive purpose: Greater repulsion was associated with lower associative-memory interference. These findings reveal that similarity between events triggers adaptive-memory distortions that minimize interference.

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