Learning-dependent gating of hippocampal inputs by frontal interneurons.

Area of Science:

• Neuroscience
• Systems Neuroscience
• Cognitive Neuroscience

Background:

• Episodic memory encoding relies on the hippocampus.
• Memory consolidation occurs in the neocortex, guided by the hippocampus.
• Hippocampal sharp wave-ripples are critical for inter-areal communication during consolidation.

Purpose of the Study:

• Investigate the synaptic and circuit basis of hippocampal-neocortical communication.
• Clarify the role of specific interneuron populations in mediating this communication during learning.

Main Methods:

• In vivo whole-cell patch-clamp recordings in the frontal neocortex.
• Local field potential recordings in CA1 of head-fixed mice.
• Chemogenetic inactivation of specific interneuron types (SOM+, PV+).
• Utilized a virtual-reality spatial navigation task.

Main Results:

• Frontal principal neurons depolarized during hippocampal ripples in trained mice.
• This depolarization and task performance were impaired by SOM+ interneuron inactivation.
• In untrained mice, ripple-associated depolarization emerged upon PV+ interneuron inactivation.

Conclusions:

• Somatostatin-positive (SOM+) interneurons disinhibit frontal principal neurons by inhibiting parvalbumin-positive (PV+) interneurons.
• This acts as a disinhibitory gate, facilitating hippocampal input to the neocortex during learning.
• This mechanism is essential for goal-directed spatial memory consolidation.