Memory allocation mechanisms underlie memory linking across time

Abstract

Memories are dynamic in nature. A cohesive representation of the world requires memories to be altered over time, linked with other memories and eventually integrated into a larger framework of sematic knowledge. Although there is a considerable literature on how single memories are encoded, retrieved and updated, little is known about the mechanisms that govern memory linking, e.g., linking and integration of various memories across hours or days. In this review, we present evidence that specific memory allocation mechanisms, such as changes in CREB and intrinsic excitability, ensure memory storage in ways that facilitate effective recall and linking at a later time. Beyond CREB and intrinsic excitability, we also review a number of other phenomena with potential roles in memory linking.

Memory engrams: Recalling the past and imagining the future

“…How do different engrams representing different events interact? The mechanisms governing neuronal allocation to an engram supporting a single event also serve to either coallocate neurons to overlapping engrams (thereby linking events) or dis-allocate neurons to nonoverlapping engrams (thereby disambiguating events) (100,(166)(167)(168). Neurons that are relatively more excitable than their neighbors at the time of an event are more likely to be allocated to the engram supporting that event memory (100).…”

Neural and neuronal discoordination in schizophrenia: From ensembles through networks to symptoms

“…To support adaptive cognition and behaviour, memories are linked so that recollection of one invokes another, related memory. The neurobiological processes of memory allocation and linking has been, to some degree, elucidated in recent years by a number of ingenious experimental studies that directly manipulated the memory trace (reviewed in). Briefly, memory is allocated to neurons with increased excitability, a process mediated by CREB.…”

“…Compared to dedicated coding by cardinal units, ensemble coding allows many more items to be remembered within a network with higher redundancy and robustness. It also permits pattern separation, pattern completion and linking different items in memory via a partial overlap between ensembles . The activity of different ensembles needs to be organized in time to prevent their simultaneous activation, which would lead to the superposition catastrophe, interference and subsequent information loss as illustrated in Figure .…”

New Tools in Cognitive Neurobiology: Biotin-Digoxigenin Detection of Overlapping Active Neuronal Populations by Two-Color c-fos Compartment Analysis of Temporal Activity by Fluorescent in situ Hybridization (catFISH)

“…This possibility would further extend the framework for simultaneous visualization of several cognitive episodes within the same brain. Thus, the protocols described here can be used for the analysis of neuronal populations activated by engagement in at least two behavior tasks, where two stages of behavioral training or testing are separated by varying time intervals [34][35][36][37], or for comparative analysis of neuronal ensembles recruited into memory acquisition and its subsequent retrieval [38].…”