Propagation of hippocampal ripples to the neocortex by way of a subiculum-retrosplenial pathway

Noam Nitzan, Sam McKenzie, Prateep Beed, Daniel Fine English, Silvia Oldani, John J Tukker, György Buzsáki and Dietmar Schmitz

Bouts of high frequency activity known as sharp wave ripples (SPW-Rs) facilitate commu-nication between the hippocampus and neocortex. However, the paths and mechanisms bywhich SPW-Rs broadcast their content are not well understood. Due to its anatomicalpositioning, the granular retrosplenial cortex (gRSC) may be a bridge for this hippocampo-cortical dialogue. Using silicon probe recordings in awake, head-fixed mice, we showthe existence of SPW-R analogues in gRSC and demonstrate their coupling to hippocampalSPW-Rs. gRSC neurons reliably distinguished different subclasses of hippocampal SPW-Rsaccording to ensemble activity patterns in CA1. We demonstrate that this coupling is brainstate-dependent, and delineate a topographically-organized anatomical pathway via VGlut2-expressing, bursty neurons in the subiculum. Optogenetic stimulation or inhibition of burstysubicular cells induced or reduced responses in superficial gRSC, respectively. These resultsidentify a specific path and underlying mechanisms by which the hippocampus can conveyneuronal content to the neocortex during SPW-Rs.

Featured images left, Figure 1. Expression of local ripple activity in the gRSC; right, Figure 8. Identification of subicular bursting cells in vivo.
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Keywords

hippocampusneural circuits
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