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What do newborns think about? The answer could be «about themselves»! Here the authors show that early neuronal activity in hippocampus of neonate rats is entrained by neuron activity in entorhinal cortex which is itself evoked by body twitches. This program could drive the maturation of circuits which later on will shift to a more internal driving mode in order to perform complex operations based on memory. (by Ingrid Bureau)

Authors: G. Valeeva, S. Janackova, A. Nasretdinov, V. Rychkova, R. Makarov, G.L. Holmes, R. Khazipov and P.-P. Lenck-Santini

Scientific abstract: Correlated activity in the entorhinal–hippocampal neuronal networks, supported by oscillatory and intermittent population activity patterns is critical for learning and memory. However, when and how correlated activity emerges in these networks during development remains largely unknown. Here, we found that during the first postnatal week in non-anaesthetized head-restrained rats, activity in the superficial layers of the medial entorhinal cortex (MEC) and hippocampus was highly correlated, with intermittent population bursts in the MEC followed by early sharp waves (eSPWs) in the hippocampus. Neurons in the superficial MEC layers fired before neurons in the dentate gyrus, CA3 and CA1. eSPW current-source density profiles indicated that perforant/temporoammonic entorhinal inputs and intrinsic hippocampal connections are coactivated during entorhinal–hippocampal activity bursts. Finally, a majority of the entorhinal–hippocampal bursts were triggered by spontaneous myoclonic body movements, characteristic of the neonatal period. Thus, during the neonatal period, activity in the entorhinal cortex (EC) and hippocampus is highly synchronous, with the EC leading hippocampal activation. We propose that such correlated activity is embedded into a large-scale bottom-up circuit that processes somatosensory feedback resulting from neonatal movements, and that it is likely to instruct the development ofconnections between neocortex and hippocampus.

Published in Cerebral Cortex, December 2018

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