A flexible hippocampal population code for experience relative to reward

Area of Science:

• Neuroscience
• Cognitive Science
• Behavioral Biology

Background:

• Memory formation relies on remembering events preceding and following rewards.
• The hippocampus, particularly CA1, is known for spatial and non-spatial memory encoding.
• It remains unclear if hippocampal activity encodes entire event sequences relative to reward.

Purpose of the Study:

• To investigate whether hippocampal CA1 activity encodes event sequences relative to reward.
• To determine how hippocampal neural ensembles represent and update reward-associated information.

Main Methods:

• Two-photon imaging of hippocampal CA1 neurons in mice navigating virtual environments.
• Monitoring neural activity during tasks with shifting hidden reward locations.

Main Results:

• A subpopulation of hippocampal neurons updated firing fields to maintain a relative position to the reward.
• This created reward-relative sequences spanning the entire task, strengthening with learning.
• Spatial environment coding was preserved by a dynamic, parallel neuronal subpopulation.

Conclusions:

• Hippocampal ensembles flexibly encode multiple experiential aspects, including reward-relative sequences.
• This neural mechanism amplifies behaviorally relevant information, crucial for adaptive behavior.
• Findings shed light on how the brain constructs and updates temporal event sequences for memory.