Hippocampal connectivity predicting recognition and categorization abilities.

Introduction: Flexible use of memory involves both the ability to form detailed memories of individual experiences (specificity) and to generalize across related experiences (generalization). Memory specificity and generalization have been attributed to distinct neocortical regions, such as ventrolateral prefrontal cortex (PFC) and ventromedial PFC respectively. The hippocampus has been traditionally associated with memory specificity, but more recent work highlights additional role in generalization. Here, we tested the hypothesis that the hippocampus supports both memory specificity and generalization, but through interactions with distinct cortical regions. Methods: Fifty-two adults learned to categorize blended face stimuli, enabling both extraction of category structure (generalization) and encoding of item-specific features (specificity). Background functional connectivity was measured using fMRI during passive viewing of the same faces before and after learning. Results: Participants showed robust category learning, above-chance recognition of studied faces from similar lures, and successful category generalization to novel category members. Recognition and categorization performance were not highly correlated, suggesting distinct processes supporting each memory function. In the brain, we found distinct connectivity profiles of anterior hippocampus, presumed to preferentially contribute to generalization, and posterior hippocampus, presumed to preferentially contribute to specificity. Learning led to increased anterior hippocampal connectivity with default mode regions including ventromedial PFC, and posterior hippocampal connectivity with visual cortex. Increased anterior hippocampal connectivity with ventromedial PFC, somatomotor cortex, and visual cortex predicted better category generalization, whereas increased posterior hippocampal connectivity with ventrolateral PFC predicted more accurate face recognition. Exploratory analyses revealed widespread learning-related changes in cortico-cortical interactions, with changes in connectivity among visual, somatomotor, and default mode networks predicting categorization. Discussion: Together, these findings support the notion that the hippocampus supports both memory specificity and generalization through interactions with distinct cortical networks. These results advance mechanistic accounts of how the hippocampus and cortex coordinate to balance competing memory demands.