Core neurons are structural crossroads of cortical dynamics

Abstract

Cortical events of correlated neuronal firing are thought to underlie sensorimotor and associative functions. In the dominant theory, events are attractors of cortical dynamics, pulled by strong mutual connections between recurrently active – core – neurons. Here, we exhaustively measured core connectivity, using a unique dataset with co-registered two-photon calcium imaging and electron microscopy of the same cortical tissue. We report that cores make fewer, weaker, mutual connections compared to other neurons. Instead, they are central to the flow of the many pathways they belong to. We present a model where cores arise from a simple distance-dependent connectivity rule, without imposed connectivity biases. Our integrated analysis shows that the link between cortical dynamics and structure is not consistent with attractors but rather with confluent connectivity pathways. Recurrently active within reproducible population events, core neurons characterize cortical activity not by virtue of strong mutual connections but by being central to many crossing pathways.