Rhinal-Hippocampal Information Flow Reverses Between Memory Encoding and Retrieval

The medial temporal lobe is crucial for the encoding and retrieval of episodic long-term memories. It is widely assumed that memory encoding is associated with information transfer from sensory regions via the rhinal cortex into the hippocampus. Retrieval of information should then be associated with transfer in the reverse direction. However, experimental evidence for this mechanism is still lacking. Here, we show in human intracranial EEG data during two independent recognition memory paradigms that rhinal-hippocampal information flow significantly changes its directionality from encoding to retrieval. Using a novel phase-based method to analyze directional coupling of oscillations, coupling values were more positive (i.e., from rhinal cortex to the hippocampus) during encoding as compared to retrieval. These effects were observed in the delta (1-3 Hz) range where rhinal-hippocampal post-stimulus phase synchronization increased most robustly across both experiments.