Functional Interactions between Entorhinal Cortical Pathways Modulate Theta Activity in the Hippocampus.

Area of Science:

• Neuroscience
• Cognitive Science

Background:

• Theta oscillations are crucial for hippocampal function in memory and exploration.
• Multiple coexisting theta rhythms in the hippocampus originate from CA3 and entorhinal cortex (EC) regions.
• Previous studies showed behavioral state modulation of theta rhythm synchrony but not information transmission.

Purpose of the Study:

• To investigate directed information transmission between hippocampal theta rhythm generators.
• To explore how novelty exploration impacts functional connectivity within the hippocampus and its afferent pathways.

Main Methods:

• Used source separation to isolate hippocampal current generators in rats.
• Applied Granger causality and transfer entropy to analyze directed interactions between theta activities.
• Recorded neural activity during exploration of familiar environments with and without novel stimuli.

Main Results:

• Novelty exploration increased theta power in EC-derived generators.
• Found directed interaction from Schaffer input to EC-III input in CA1.
• Observed bidirectional interaction between EC-derived inputs (EC-II and EC-III).
• Novelty increased EC-II influence over EC-III, while Schaffer influence decreased.

Conclusions:

• Hippocampal theta activity and synchrony during novelty are linked to increased directed functional connectivity from EC-II to EC-III.
• Findings elucidate the flow of information between entorhinal cortex and hippocampus during memory updating and exploration.