Summary: New research from RIKEN shows that astrocytes — not neurons alone — play a central role in stabilizing emotionally charged memories. After a stressful event such as fear conditioning, small groups of astrocytes become biologically marked by upregulating adrenoreceptors, making them responsive when the memory is later reactivated.
Interrupting these astrocytes during recall weakens memory stability, while artificially activating them amplifies fear responses and causes overgeneralization. These results reveal an unexpected cellular mechanism that helps explain how emotionally intense experiences persist and suggest new therapeutic directions for PTSD and trauma-related disorders.
Key facts:
- Astrocyte tagging: Emotional events trigger expression of adrenergic receptors in a subset of astrocytes, marking them for later re-engagement.
- Memory stabilization: Those tagged astrocytes are reactivated at recall and contribute to long-term memory persistence and precision.
- Therapeutic potential: Modulating astrocytic activity could offer targeted ways to reduce the emotional impact of traumatic memories without erasing other memories.
Source: RIKEN
Why do we remember only some past experiences?
A team led by Jun Nagai at the RIKEN Center for Brain Science investigated why some experiences, especially emotionally salient ones, remain stable over time while others fade. Their study, published in Nature, identifies a key role for astrocytes — a class of glial cells traditionally viewed as supportive — in stabilizing emotional memories.
Rather than being passive bystanders, particular astrocytes are transcriptionally altered after an emotionally intense event. Over the days that follow, these astrocytes increase expression of alpha and beta adrenoreceptors, becoming more sensitive to noradrenaline. When the related memory is later recalled, coincident signals from local neuronal engrams and long-range noradrenergic inputs trigger those primed astrocytes to produce the activity marker Fos, and this repeated astrocytic engagement supports memory stabilization.
To observe this process across the brain, the researchers developed a selective Fos-tagging system that labels active astrocytes (but not neurons) during a defined time window. Using this tool in mice trained to associate a specific cage with an unpleasant experience, they compared astrocyte and neuronal activity during initial learning and during later recall.
A striking result was that Fos activity in astrocytes was minimal during learning but pronounced during recall, whereas neuronal engram activity and noradrenergic signaling occur during both phases. Single-cell RNA sequencing revealed why: after the emotionally charged event, astrocytes upregulate adrenoreceptors across a multiday window, effectively creating a cellular tag that makes them eligible to respond to future recall.
Functional experiments confirmed the causal role of these astrocytes. Temporarily blocking signaling in the Fos-positive astrocyte population during recall destabilized the memory; mice failed to show the expected fear response. Conversely, forcing activation of these astrocytes during recall exaggerated fear reactions, made mild aversive cues seem severe, and induced generalization to contexts that had never been paired with harm.
These findings point to an astrocytic “memory switch” that selectively reinforces emotionally salient, repeated experiences. Jun Nagai and colleagues suggest this mechanism may underlie persistent or overgeneralized memories in conditions like PTSD and that targeting astrocytic signaling could allow therapies that dampen traumatic memories while preserving other memories.
Beyond neuroscience applications, Nagai notes that the astrocyte-tagging mechanism could inspire more efficient memory strategies in artificial intelligence: by selectively storing and prioritizing experiences based on salience and recurrence, systems could reduce energy use while retaining context-relevant information.
The research team plans to investigate how astrocytes become “eligible” to gate memory stabilization and whether specific memory types can be selectively enhanced or suppressed by manipulating these astrocytic ensembles.
Key questions answered:
A: They found that astrocytes are transcriptionally marked after emotional experiences and later re-engage during recall to stabilize those memories.
A: Emotional intensity drives upregulation of adrenergic receptors in specific astrocytes, tagging them to respond when the corresponding memory trace is reactivated.
A: It reveals a non-neuronal mechanism for memory persistence and suggests potential avenues for treating PTSD by attenuating the emotional severity of traumatic memories without erasing memory content.
About this neuroscience and memory research news
Author: Adam Phillips
Source: RIKEN
Contact: Adam Phillips – RIKEN
Image: The image is credited to Neuroscience News
Original research: Open access. “The astrocytic ensemble acts as a multiday trace to stabilize memory” by Jun Nagai et al., published in Nature.
Abstract
The astrocytic ensemble acts as a multiday trace to stabilize memory
Recalled memories become temporarily labile and must be restabilized. The mechanism that preserves memories of survival-relevant, emotionally salient, and repeated experiences has been unclear. This work identifies an astrocytic ensemble that is transcriptionally primed by emotional experience and functionally engaged by repeated recall to stabilize such labile memories.
Using a brain-wide Fos-tagging and imaging approach that selectively labels active astrocytes, the authors show that astrocytic Fos ensembles are preferentially recruited in regions containing neuronal engrams and are more prominent during fear recall than during initial conditioning. The induction of the astrocytic ensemble involves a two-step process: an initial fear event triggers slow, day-long astrocytic state changes including upregulation of noradrenaline receptors; subsequent recall produces enhanced noradrenergic responses that allow these primed astrocytes to integrate local engram signals with long-range neuromodulatory input, driving secondary state changes such as Fos expression and secretion of modulatory factors like IGFBP2.
Pharmacological and genetic perturbations of astrocytic ensemble signaling alter engram activity and affect both memory stability and precision. Thus, a subset of astrocytes forms a multiday trace after experience-dependent neural activity, making them eligible to capture future repeated experiences and stabilize memory.