Summary: Researchers have found that rats strengthen memories of negative events that occur in familiar locations by selectively replaying those experiences during rest. These memories become associated with a mental map created by place cells in the hippocampus, and exposure to an aversive event causes some of those place cells to change their activity to register the negative experience.
The study shows that place cells tied to an unpleasant event are preferentially reactivated during pauses between trials, suggesting a replay mechanism that reinforces the memory. These results shed light on how episodic details are added to existing spatial representations and could inform new approaches to psychiatric conditions such as post-traumatic stress disorder (PTSD).
Key Facts:
- Rats reinforce memories of negative experiences occurring in familiar places by repeatedly replaying those events during rest.
- The neurons that register aversive experiences are distinct yet adjacent to canonical place cells within the hippocampus.
- Because aversive-event–linked place cells are reactivated more during rest, the findings may help researchers better understand how traumatic memories are encoded and suggest directions for PTSD research.
Source: RIKEN
Three neuroscientists at RIKEN report that rats selectively replay negative experiences in familiar locations, reinforcing those memories.
When animals explore a new environment they form an internal spatial map. This map depends on specialized hippocampal neurons called place cells, each of which becomes active when the animal occupies—or remembers—specific locations. The mapping process is well established, but less is known about how experiences that occur within an already-mapped space are incorporated into that representation.
Everyday experience suggests we selectively retain important events tied to places while letting unimportant details fade. As the researchers explain, a hiker may not remember every mile of a familiar trail, but a rare, threatening encounter—such as an animal attack—leaves a vivid record of both the event and its surroundings. The study aimed to clarify how such salient episodic content becomes attached to a spatial map.
Joshua Johansen, Jake Ormond, and Simon Serka examined how place-cell activity changes when rats encounter aversive stimuli within a known environment. They observed that a subset of place cells “remapped” during learning: these cells shifted their firing fields to encode the negative event. Other place cells remained stable, preserving a reliable representation of the environment’s physical layout.
Crucially, the remapped cells associated with the aversive experience were more likely than stable cells to be reactivated during rest periods between trials. These reactivations occurred in association with sharp-wave ripple events and replay sequences—neural phenomena that are thought to support memory consolidation. The preferential replay of remapped cells suggests a mechanism by which new, emotionally salient information is integrated into an existing spatial map.
The findings were published in The Journal of Neuroscience and point to broader implications for understanding memory processes in health and disease. Johansen and colleagues note that while simple forms of fear learning have been well studied, treatments for disorders such as PTSD remain limited. A better understanding of how higher-order systems like the hippocampus alter and preserve records of unpleasant experiences could help reveal how these systems become dysregulated in psychiatric conditions and guide future therapeutic strategies.
About this memory and PTSD research news
Author: Joshua Johansen
Source: RIKEN
Contact: Joshua Johansen – RIKEN
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Enhanced Reactivation of Remapping Place Cells during Aversive Learning” by Joshua Johansen et al. Journal of Neuroscience
Abstract
Enhanced Reactivation of Remapping Place Cells during Aversive Learning
Research on hippocampal place cells has clarified how the brain encodes the layout of distinct places, but it remains unclear how episodic memories that occur within familiar environments are added to those maps. The authors developed a spatial decision-making task in which male rats learned to navigate a multiarm maze to obtain food while avoiding arms that delivered aversive stimuli. Learning induced partial remapping in CA1 place cells, creating two identifiable populations: remapping cells and stable cells. During rest, remapping cells were recruited into sharp-wave ripples and replay events more often than stable cells, even though both populations showed similar firing rates during navigation. These results suggest that selective recruitment into replay and ripple-associated events provides a mechanism for integrating new contextual information into an already established spatial representation.