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

Lopez-Madrona, V.; Pérez-Montoyo, E.; Álvarez-Salvado, E.; Moratal, D.; Herreras, O.; Pereda, E.; Mirasso, C.; Canals, S.
eLife , (2020)

Hippocampal firing is organized in theta sequences controlled by internal memory processes and by external sensory cues, but how these computations are coordinated is not fully understood. Although theta activity is commonly studied as a unique coherent oscillation, it is the result of complex interactions between different rhythm generators. Here, by separating hippocampal theta activity in three different current generators, we found epochs with variable degrees of theta phase coupling, suggesting flexible interactions between them. We found that epochs of highly synchronized theta rhythmicity preferentially occurred during behavioral tasks requiring coordination between internal memory representations and incoming sensory information. In addition, we found that gamma oscillations in specific frequency bands were associated with specific theta generators and maximally when theta generators were synchronized. We propose a mechanism for segregating or integrating hippocampal computations based on the coexistence of different theta-gamma frameworks that flexibly couple or decouple accommodating the cognitive needs.

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