Arc/Arg3.1 mRNA global expression patterns elicited by memory recall in cerebral cortex differ for remote versus...

Area of Science:

• Neuroscience
• Cognitive Science
• Molecular Biology

Background:

• The neocortex is crucial for forming and storing long-term declarative memories.
• Mechanisms of systems consolidation and memory storage sites remain poorly understood.
• Identifying enduring memory correlates (mnemonic plasticity) is challenging.

Purpose of the Study:

• To map neuronal activity during recall of recent and remote spatial memories in rats.
• To identify specific cortical regions involved in memory consolidation and storage.
• To investigate mnemonic plasticity by analyzing Arc gene expression patterns.

Main Methods:

• Rats were trained on a spatial water-maze task.
• Arc/Arg3.1 (Arc) mRNA expression, a marker of neuronal activity, was mapped after recent (24h) and remote (1 month) memory recall.
• Expression patterns were compared between memory recall, swimming, and naive controls.

Main Results:

• Arc expression was significantly higher after recent memory recall than remote recall.
• While some cortical areas showed decreased Arc expression for remote memories, others (prefrontal, retrosplenial) maintained robust expression.
• Both recent and remote recall showed similar upper cortical layer Arc expression increases, but layer 6 decreased only after recent recall.

Conclusions:

• Remote memory recall engages fewer cortical segments with overall lower neuronal activity compared to recent memory recall.
• This reduced activity pattern presents challenges in detecting storage sites and plasticity for remote memories.
• Arc mapping offers a potential method to overcome these detection difficulties.