<jats:title>Abstract</jats:title>
<jats:p>
Recalled memories become transiently labile and require stabilization
<jats:sup>1–3</jats:sup>
. The mechanism for stabilizing memories of survival-critical experiences, which are often emotionally salient and repeated, remains unclear
<jats:sup>4</jats:sup>
. Here we identify an astrocytic ensemble that is transcriptionally primed by emotional experience and functionally triggered by repeated experience to stabilize labile memory. Using a novel brain-wide
<jats:italic>Fos</jats:italic>
tagging and imaging method, we found that astrocytic
<jats:italic>Fos</jats:italic>
ensembles were preferentially recruited in regions with neuronal engrams
<jats:sup>5</jats:sup>
and were more widespread during fear recall than during conditioning. We established the induction mechanism of the astrocytic ensemble, which involves two steps: (1) an initial fear experience that induces day-long, slow astrocytic state changes with noradrenaline receptor upregulation; and (2) enhanced noradrenaline responses during recall, a repeated experience, enabling astrocytes to integrate coincident signals from local engrams and long-range noradrenergic projections, which induce secondary astrocytic state changes, including the upregulation of
<jats:italic>Fos</jats:italic>
and the neuromodulatory molecule IGFBP2. Pharmacological and genetic perturbation of the astrocytic ensemble signalling modulate engrams, and memory stability and precision. The astrocytic ensemble thus acts as a multiday trace in a subset of astrocytes after experience-dependent neural activity, which are eligible to capture future repeated experiences for stabilizing memories.
</jats:p>
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