Hippocampus shapes entorhinal cortical output through a direct feedback circuit

Area of Science:

• Neuroscience
• Systems Neuroscience
• Cognitive Neuroscience

Background:

• Cortico-hippocampal interactions are crucial for integrating information and memory.
• The feedback circuits from the hippocampus to the cortex are less understood than the forward pathways.

Purpose of the Study:

• To investigate the organization and function of hippocampus-to-cortex feedback pathways.
• To elucidate the circuit mechanisms underlying cortico-hippocampal interplay in memory processing.

Main Methods:

• Circuit mapping in mice using anatomical tracing and electrophysiology.
• Two-photon imaging during behavioral tasks (navigation).
• Induction of synaptic plasticity (homosynaptic and heterosynaptic).

Main Results:

• Identified two parallel hippocampus-to-entorhinal cortex feedback pathways: a disynaptic route to layer 5 and a monosynaptic input to layer 2/3.
• Hippocampal inputs differentially modulate cortical layers: excitation in layer 5 and feed-forward inhibition in layer 2/3.
• Synaptic plasticity differed between pathways; layer 5 showed potentiation, layer 2/3 showed heterosynaptic plasticity and spike output.
• Layer 5 inputs support memory encoding, while layer 2/3 inputs support memory recall.
• Hippocampal feedback influences spatially tuned cortical activity during navigation.

Conclusions:

• Hippocampal feedback to the cortex comprises functionally distinct parallel pathways.
• These pathways play differential roles in memory encoding and recall.
• Hippocampal feedback iteratively shapes cortical processing and spatial representations.