Astroengrams: rethinking the cellular substrate for memory

Our understanding of memory and learning has been largely overshadowed by neurocentric studies, leaving non-neuronal cells out of the equation. The cellular substrate for memory is thought to lie within engrams - ensembles of neurons that activate during learning, whose reactivation leads to recall of the acquired memory. Astrocytes are now taking centre stage in the modulation of memory and other cognitive functions. Contrary to widespread assumptions, these glial cells activate as sparse groups, or ensembles, and reactivation of astrocyte ensembles recruited during learning produces recall. Recent advances using activity-dependent tools to interrogate the roles of astrocytes in memory support a paradigm shift: engrams not only are composed of neurons but also include astrocyte ensembles that activate during learning, forming what we call 'astroengrams'. Thus, the coordinated activity of neuronal and astrocytic engrams provides an integrated framework to orchestrate memory storage and recall.