Stable Network Motifs with Divergent Engagement Across Memory Outcomes

Abstract

Visual recognition memory depends on coordinated interactions across distributed medial temporal, prefrontal, and limbic networks, yet the sub-second large-scale network dynamics distinguishing successful from unsuccessful recognition remain poorly understood. Here we used intracranial EEG recordings from seven patients (4 female, 3 male) with medically refractory epilepsy performing a new-old visual recognition memory task to characterize time-resolved directed functional connectivity and dynamic network organization. Directed effective connectivity was estimated using bivariate Granger causality in a sliding-window framework, and dynamic community structure was identified using the Louvain modularity algorithm. Successful recognition (Hits) was associated with a qualitatively distinct network configuration: low modularity (Q = 0.05 vs. 0.09-0.15 in other conditions), a cross-hemispheric community structure integrating left medial temporal lobe (MTL) with right prefrontal cortex, and sustained network integration throughout the post-stimulus period. Right-hemisphere nodes within this cross-hemispheric community showed stronger within-community directed connectivity than left-hemisphere nodes (mean asymmetry index = 0.33, p < 0.001), consistent with right prefrontal dominance in driving network integration during successful retrieval. In contrast, Correct Rejections were characterized by early transient network segregation (onset 32 ms) dominated by right-hemisphere activity. Hub regions were non-overlapping across conditions--left-lateralized during Hits, right-lateralized during Correct Rejections. These findings imply that successful visual recognition is distinguished not by stronger connectivity per se, but by a reorganization of large-scale network topology that transiently integrates left MTL with right prefrontal cortex into a unified functional community.