The role of dorsal-ventral hippocampal dynamics in sleep-dependent processing of aversive experiences

Creating internal representations of the surrounding context and stabilizing them are essential for safe exploration of the environment. Spatial memories in the dorsal hippocampus (dHPC) are initially encoded by place-cells during awake exploration and stabilized during non-REM sleep fast oscillations (sharp-wave ripples) through place cell reactivation. The hippocampal formation is heterogeneous; the dHPC processes mostly contextual information, while the ventral part (vHPC) encodes valence and anxiety. This functional segregation is supported by the stronger connectivity of the vHPC with other structures of the valence-processing networks We propose that dorsal-ventral communication during wakefulness and sleep is involved in the encoding and subsequent consolidation of emotional memories, potentially integrating or segregating context and valence information. To test this, we recorded the electrophysiological activity in the dHPC and vHPC in rats during reward and aversion-motivated exploration of a linear track and subsequent sleep. Focusing on ripples and neuronal assemblies, we show that dorso-ventral dynamics differ between aversive vs. reward-motivated explorations and the subsequent non-REM sleep epochs. These changes in dorso-ventral hippocampal functional communication might sustain the encoding and selective reactivation of experiences based on their emotional valence.