Local memory allocation recruits memory ensembles across brain regions

Memories are thought to be stored in ensembles of neurons across multiple brain
regions. However, whether and how these ensembles are coordinated at the time of
learning remains largely unknown. Here, we combined CREB-mediated memory
allocation with transsynaptic retrograde tracing to demonstrate that the allocation of
aversive memories to a group of neurons in one brain region directly affects the
allocation of interconnected neurons in upstream brain regions in a behavioral- and
brain region-specific manner. Our analysis suggests that this cross-regional
recruitment of presynaptic neurons is initiated by downstream memory neurons
through a retrograde mechanism. Together with statistical modeling, our results
indicate that in addition to the anterograde flow of information between brain regions,
the establishment of interconnected, brain-wide memory traces relies on a retrograde
mechanism that coordinates memory ensembles at the time of learning.