16 avril 2021

Institut de Neurosciences des Systèmes (INS)

Different theta frameworks coexist in the rat hippocampus and are coordinated during memory-guided and novelty tasks

Invité par Nicole MALFAIT

Résumé :

Theta-gamma cross-frequency coupling (CFC) is thought to route information flow in the hippocampus. How this idea copes with the co-existence of multiple theta rhythm generators is not well understood. Using independent component analysis on electrophysiological recordings we have analyzed multiple theta and gamma activities in the rat hippocampus to unveil the dynamic synchronization of theta oscillations across hippocampal layers, and its differential coupling to pathway-specific gamma frequency bands. We found that theta-gamma CFC is stronger between oscillations originated in the same hippocampal layer. Interestingly, strong CFC was linked to theta phase locking across layers in a behaviourally related manner, being higher during memory encoding and retrieval. Systematic analysis of cross-frequency directionality suggested that the amplitude of gamma oscillations sets the phase of theta in all pathway-specific theta-gamma pairs. These results suggest, contrary to an extended assumption, that pathway- and band-specific gamma-oscillations coordinate theta rhythms. This mechanism may explain how anatomically distributed computations, organized in theta waves, can be bound together.

Bios : Víctor López did his PhD at the Neuroscience Institute of Alicante, Spain, under the supervision of Dr. Santiago Canals. During his PhD, he studied the electrophysiological activity of the rat hippocampus in memory, focusing on the interaction between theta and gamma oscillations. Parallelly, he worked at the IFISC (Mallorca, Spain) with Dr. Claudio Mirasso, analyzing the functional connectivity between hippocampus and entorhinal cortex with computational models. He finalized his PhD at the Cajal Institute in Madrid with Dr. Óscar Herreras, where he realized all the opportunities that the independent component analysis offers to disentangle neurophysiological sources, finding that the theta rhythm can be separated into three main generators inside the hippocampus. Now, he is doing a post-doc at the INS in Marseille where he uses the independent component analysis to study the similarities between intracerebral EEG and MEG during memory tasks.

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