NL
DE
Why do some memories stay vivid and detailed for a long time, while others fade into vague impressions? A new study led by Kübra Gülmez Karaca in the research groups of Benno Roozendaal and Marloes Henckens from Radboudumc and the Donders Institute may offer part of the answer.
The research, just published in Neuropsychopharmacology, shows that noradrenergic activation - a response to emotional arousal- right after learning can help preserve the rich, episodic quality of memories over time, meaning to precisely remember what happened when and where.
The team employed a memory task in mice that mimics the way humans remember specific locations of objects in certain contexts, such as memorizing the location of the kitchen table in the kitchen and sofa in the living room in a new house. Mice normally forget these associations within two weeks. When the researchers gave the mice a dose of yohimbine, a drug that increases noradrenaline levels in the brain, immediately after learning, they still showed precise memory for the original object-context combinations even after two weeks.
To understand the brain mechanisms that underlie the precision of memory over time, the researchers used a genetically engineered mouse line that allowed them to trace the activity of memory-related neurons, generally known as “engram neurons”. They found that in the control group, memory-related neurons were initially active in the hippocampus, a brain region allowing episodically rich and detailed memory recall, whereas over time this activation shifted to the prefrontal cortex- a brain region involved in more generalized forms of memory. In contrast, in the yohimbine-treated mice, activity of memory-related neurons in the hippocampus remained even when the memory was tested two weeks later. This suggests that the noradrenergic boost upon emotional arousal helped to keep the detailed version of the memory by strengthening connections within the hippocampus.
The findings of this study could be relevant for conditions in which memory fades away too quickly or is too persistent. For example, they could be followed up in human behavioral studies combining low-dose noradrenergic stimulants with behavioral interventions in memory-impaired or trauma-exposed populations. Moreover, by showing that noradrenergic stimulants after learning can shape how memories evolve over time, this research opens up new ways to further understanding how emotional experiences are stored in the brain and remain vivid over time.
This research is part of Radboudumc Research Program: Stress and mental health program
About the publication
Gulmez Karaca K, Bahtiyar S, van Dongen L, Wolf OT, Hermans EJ, Henckens MJAG, Roozendaal B. Posttraining noradrenergic stimulation maintains hippocampal engram reactivation and episodic-like specificity of remote memory. Neuropsychopharmacology. 2025. https://doi.org/10.1038/s41386-025-02122-2
