The Path Of Remembrance: From a Past Event To Reactivation In The Brain

For something to be considered a true memory, it needs to be connected to a real event from the past. Scientists describe how the brain records and reactivates memories through patterns of neural activity called engrams, especially involving the hippocampus. The process of remembering involves reconstruction, not exact reproduction, mixing old information with general knowledge and current context. The text also explains how memories change over time and can become distanced from the original episode.

Memory is a complex process that depends on both the functioning of the mind and the brain. In this article, researchers from the University of Texas at Dallas discuss how cognitive neuroscience, the area that studies how the brain produces mental functions, understands memory representations, especially episodic memory.

This type of memory stores experiences we have lived personally, such as a birthday or an important conversation. The main idea is to understand how these memories are constructed, stored, and reactivated over time.

A central point is the difference between active and latent memory representations. Active representations are those that are "switched on" at the moment we remember something and have a direct influence on how we think or behave. Latent representations, on the other hand, are memory traces that remain stored and do not directly influence consciousness until they are activated.

According to the authors, a representation can only be called a "memory" if it has a true causal link to a past event; that is, if it truly originated from that event and not merely from imagination, assumptions, or subsequent inferences.

To explain how this causal connection works, the authors use a model called reinstatement. In simple terms, this model states that remembering something means reactivating, in the brain, patterns of neural activity that were activated when we experienced the event.

This reactivation is not a perfect copy of the original experience, but a reconstruction based on what was recorded. This process helps to understand how memories can be both faithful and distorted.

Neuroscience describes these representations at the level of brain cells. When we experience an event, certain networks of neurons, called engrams, activate and record the pattern of the experience.

An engram is a network of neurons that "stores" the pattern of an event. When something happens:

1- The hippocampus observes patterns in the neocortex.

2- It “pastes” these patterns onto a temporary trace.

3- Over time, this pattern is stabilized in the neocortex (consolidation).

It's like taking a screenshot of the emotional and sensory experience, storing a compressed version, and then reopening the file when needed..

Episodic memory retrieval involves the reactivation of cognitive and neural processes that were active when the event was initially experienced. During encoding, neural patterns are indexed and stored by the hippocampus, and hippocampus-mediated pattern separation processes ensure that similar episodic events are stored as non-overlapping memory representations. Subsequently, a retrieval cue that partially overlaps the neural pattern triggered by the original event triggers hippocampal pattern completion, resulting in the reactivation of the neural activity originally triggered by the episode during encoding.

The hippocampus, a deep brain structure, plays a key role: it coordinates these patterns and helps to "record" more stable versions in the neocortex, the outer layer of the brain where long-lasting memories reside. When we remember, part of this pattern is reactivated, constituting the neural representation of that memory.

The authors also explain that the content of an active memory does not come solely from the original experience. Often, our minds mix information retrieved from the past with semantic elements (general knowledge), mental schemas (common patterns), and even inferences based on the current context.

This means that memories are, in part, reconstructions, not exact reproductions. The older the event, the greater the chance that successive recodings have altered its original form.

Finally, the article discusses how memories can be modified over time, whether through repeated reconstructions, the influence of emotions, new information, or normal biological processes. These transformations can bring the memory closer to or further away from the original event, making some memories less precise, even though they may still seem true to the person recalling them.

This type of research helps explain, from a clinical point of view, why Alzheimer's patients remember the distant past but forget the recent past. It also explains why traumatic memories are intrusive, and how false memories arise.

From a legal perspective, it helps to understand why testimonies can be distorted even unintentionally. From a developmental perspective, it helps to understand why children's memories are more susceptible to editing. Finally, from a technological perspective, it helps to build AI inspired by human memory and how to create artificial reconsolidation systems.

READ MORE:

The cognitive neuroscience of memory representations

Michael D. Rugg, and Louis Renoult

Neuroscience & Biobehavioral Reviews, Volume 179, December 2025, 106417

https://doi.org/10.1016/j.neubiorev.2025.106417

Abstract:

The present paper considers the cognitive neuroscience of memory from a representational perspective with the aim of shedding light on current empirical and theoretical issues. We focus on episodic memory, differentiating active versus latent, and cognitive versus neural memory representations. We adopt a causal perspective, according to which a memory representation must have a causal connection to a past event to count as a memory. We note that retrieved episodic information may nonetheless only partially determine the content of an active memory representation, which can comprise a combination of the retrieved information with semantic, schematic and situational information. We further note that, especially in the case of memories for temporally remote events, re-encoding operations likely lead to a causal chain that extends from the original experience of the event to its currently accessible memory trace. We discuss how the reinstatement framework provides a mechanistic basis for the causal linkage between an experience, the memory trace encoding it, and the episodic memory of the experience, highlighting the crucial role of hippocampal engrams in encoding patterns of neocortical activity that, when active, constitute the neural representation of an episodic memory. Finally, we discuss some of the ways in which a memory can become modified and hence distanced from the episode that precipitated it.