Higher-order hub cells involved in feedforward motifs as critical factors in epileptic network instability

Abstract Sixty-five million people suffer from epilepsy and associated cognitive decline worldwide. Therefore, there is urgent need to identify novel mechanisms involved in epileptic network instability. Densely connected “hub” neurons have been implicated as key controllers of developmental as well as epileptic circuits. While such hub cells are traditionally defined by connection count, how these connections contribute to interictal dynamics is not understood. We performed whole-brain single-cell calcium imaging of the larval zebrafish brain in an acute seizure model. Biologically constrained modeling of cell-cell effective interactions successfully reproduced experimental calcium dynamics and enabled hub identification. Simulated perturbation of single hub neurons in the preseizure state confirmed that such traditional hub cells can exert major influence over global dynamics. Novel higher-order graph analytics revealed that the sensitivity to perturbation is not simply linked to outgoing degrees but rather to overexpression of feedforward motifs surrounding the hub cells that enhance downstream excitation. Model- and species similarity of the key findings was supported by similar results from the hippocampus of chronically epileptic mice. Collectively, these data identify a specific class of high-order hub neuron that is richly involved in feedforward motifs as an attractive new target for seizure control. Highlights Whole brain single-cell calcium imaging in zebrafish combined with effective connectivity modeling was used to study epileptic network instability Preseizure whole brain networks were more sensitive to simulated targeted perturbation of single richly connected “hub” neurons Higher-order graph clustering revealed overexpression of a class of hub cells engaged in feedforward motifs in the unstable preseizure state Such higher-order hub neurons enhanced downstream excitation and were causally linked to network instability Higher-order hub cells were identified in the hippocampus of chronically epileptic mice, showing similar findings across models and species.