Pre-existing and emergent cortical neuronal assembly sequences during learning.

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Systems Neuroscience

Background:

• Neuronal assemblies, defined as groups of co-active neurons, are crucial for memory consolidation and retrieval.
• In the hippocampus, neuronal assemblies can pre-exist learning and contribute to memory via sequential activation.
• It remains unclear if similar principles govern memory storage in higher cortical areas like the orbitofrontal cortex (OFC).

Purpose of the Study:

• To investigate the role and dynamics of neuronal assemblies in the orbitofrontal cortex (OFC) during cue-reward memory acquisition and maintenance.
• To determine if OFC assemblies pre-exist learning and exhibit sequential activation patterns similar to those observed in the hippocampus.
• To uncover circuit motifs enabling flexible memory storage in the cortex.

Main Methods:

• Utilized a novel ground truth-validated clustering approach to analyze neuronal activity.
• Longitudinally tracked the activity of mouse OFC neurons during cue-reward memory tasks.
• Identified and characterized distinct sequential activation dynamics within neuronal assemblies.

Main Results:

• Neuronal assemblies active after learning were found to pre-exist the learning process.
• Two distinct sequential dynamics were observed, indicative of memory consolidation and retrieval.
• Consolidation sequences emerged during the learning phase, while retrieval sequences partially involved pre-existing reward-related sequences.

Conclusions:

• Orbitofrontal cortex (OFC) learning involves the flexible recruitment of pre-existing neuronal networks.
• These networks are repurposed to form new associations, supporting flexible memory storage.
• The study reveals circuit motifs in the OFC that may underlie cortical memory formation and flexible recall.