Neuronal dynamics supporting formation and recombination of cross-modal olfactory-tactile association in the rat hippocampal formation

The present study is aimed at describing some aspects of the neural dynamics supporting discrimination of olfactory-tactile paired-associated stimuli during acquisition of new pairs and during recombination of previously-learned pairs in the rat. To solve the task, animals have to identify one odor-texture (OT) combination associated with a food reward among three cups with overlapping elements. Previous experiments demonstrated that the lateral entorhinal cortex (LEC) is involved in the processes underlying OT acquisition while the dorsal hippocampus (DH) is selectively involved in the recombination processes. In the present study, local field potentials were recorded form the anterior piriform cortex (aPC), the LEC and the DH in freely moving rats performing these tasks. Signal analysis focused on theta (5-12 Hz) and beta band (15-40 Hz) oscillatory activities both in term of amplitude and synchrony. The results showed that cue sampling was associated with a significant increase in the beta band activity during the choice period in both the aPC and the LEC, and is modulated by level of expertise and animal's decision. In addition, this increase was significantly higher during the recombination when compared to the acquisition of the OT task, specifically when animals had to neglect the odor previously associated with the reward. Finally, a significant decrease in coherence in the theta band between LEC and DH was observed in the recombination but not in the acquisition task. These data point to specific neural signatures of simple and complex cross-modal sensory processing in the LEC-DH complex.

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