Recent and remote memory recalls modulate different sets of stereotypical interlaminar correlations in Arc/Arg3.1 mRNA expression in cortical areas

Detailed organization of interlaminar relations in neuronal activity underlying recent and remote memory recall is unknown but essential for deciphering interlaminar connections involved in systems-level memory consolidation and permanent information storage. We mapped Arc/Arg3.1 (Arc) mRNA expression, a neuronal activity marker, at multiple rostro-caudal levels of the brain in Wistar rats following a platform search in a water-maze task. Strength of interlaminar correlations in Arc expression and modulation of the strength by memory recall in sensory, motor and association cortical areas were measured at 24 h and 1 month in memory retention. In order to estimate the extent of modular organization in neocortical function underlying memory recall, we studied multiple profiles of interlaminar coupling. At the level of cortical areas, we captured two robust stereotypical laminar patterns for distribution of strong and weak interlaminar correlations. These patterns emerged during both control swimming and navigation, at both retention delays. Within limits of these patterns, we established task-, time- and area-dependent modulations of the Arc correlations. Relative to swimming control, during memory recall, changes in strength of analogous interlaminar relations occurred largely in parallel but recent and remote recall modulated mostly distinct correlations. An effective remote memory recall was accompanied by fewer strengthened correlations as compared to recent recall. Thus, a behavioral experience is accompanied by a well-ordered or stereotypical spatial organization of interlaminar relations in neuronal activity distribution. Interlaminar correlations in Arc expression modulated by recent and remote memory recall could guide future inactivation and detection studies necessary to decipher interlaminar connections involved in systems-level consolidation and to reveal mnemonic plasticity specific to spatial memory.

Research Highlights
► Laminar patterns for strong and weak Arc interlaminar correlations are similar across the cortex.
► Memory recall induces parallel modifications in analogous Arc correlations.
► Recent and remote recalls modify different sets of Arc interlaminar correlations.
► Remote recall strengthens fewer Arc correlations compared to recent recall.