Asymmetric Frequency-Specific Feedforward and Feedback Information Flow between Hippocampus and Prefrontal Cortex...

Area of Science:

• Neuroscience
• Cognitive Science
• Electrophysiology

Background:

• Hippocampus and prefrontal cortex (PFC) circuits are crucial for human episodic memory.
• The precise electrophysiological basis of directed information flow between these regions during memory formation remains unclear.
• Previous fMRI studies show coactivation but lack electrophysiological detail on dynamic interactions.

Purpose of the Study:

• To investigate nonlinear causal interactions between the hippocampus and lateral PFC during verbal memory encoding and recall.
• To elucidate the directionality, frequency specificity, and timing of information flow between these brain regions.
• To understand the electrophysiological underpinnings of asymmetric signaling in episodic memory.

Main Methods:

• Intracranial EEG recordings from 26 participants (16 females) performing verbal memory tasks.
• Direction-specific information theoretic analysis to quantify causal interactions.
• Frequency band analysis (delta-theta, beta) and propagation delay estimation.

Main Results:

• Causal information flow was significantly higher from the hippocampus to the PFC than vice versa.
• This asymmetric flow was observed during both memory encoding and recall, and was greater than during rest.
• Hippocampus-to-PFC flow was dominant in the delta-theta bands (0.5-8 Hz), while PFC-to-hippocampus flow was stronger in the beta band (12-30 Hz).
• Estimated propagation delay was 17.7 ms, consistent with monosynaptic influence.

Conclusions:

• Distinct asymmetric feedforward (hippocampus to PFC) and feedback (PFC to hippocampus) signaling mechanisms exist between these regions.
• These mechanisms play dissociable roles in memory recall, utilizing different frequency channels.
• The findings offer novel insights into the electrophysiological basis of directed information flow in human episodic memory formation.