Spaced training enhances memory and prefrontal ensemble stability in mice

Area of Science:

• Neuroscience
• Cognitive Science
• Memory Research

Background:

• The spacing effect demonstrates that learning is improved when study sessions are distributed over time.
• The underlying neuronal mechanisms of the spacing effect, particularly how it impacts neuronal ensembles, remain largely uninvestigated.

Purpose of the Study:

• To investigate the effects of trial spacing on the stability and size of neuronal ensembles involved in memory.
• To determine if spaced learning influences the population activity patterns of neurons during memory encoding and retrieval.

Main Methods:

• Mice were trained on a delayed matching-to-place task to assess memory performance under different trial spacing conditions.
• c-Fos labeling and chemogenetic inactivation were used to identify the role of the dorsomedial prefrontal cortex (dmPFC).
• In vivo calcium imaging monitored the activity of dmPFC excitatory neurons during spaced learning.

Main Results:

• A 60-minute trial spacing interval resulted in more robust memory formation compared to shorter or longer intervals.
• The dorsomedial prefrontal cortex (dmPFC) was confirmed to be involved in memory storage.
• Longer trial spacing led to increased similarity in population activity patterns during encoding and retrieval, without altering the size of neuronal ensembles.

Conclusions:

• Spaced learning enhances memory robustness by promoting the reactivation and stabilizing the activity patterns of prefrontal neuronal ensembles.
• The findings suggest that the spacing effect on memory is mediated by changes in neuronal ensemble dynamics rather than alterations in ensemble size.