Complementary white matter networks support flexible concept learning.

Introduction: Concept learning is not an isolated act of cognition; it recruits a host of core mechanisms, including working memory, decision making, and attention. A wide range of brain networks spanning cortical and subcortical areas support these operations, which have been identified via activation patterns related to concept learning. A critical open question, however, is whether the white matter architecture connecting these regions serves as the structural scaffold that makes such flexible learning possible. Methods: We employed a rule-plus-exception learning paradigm wherein participants categorized visually complex stimuli. While some items closely followed the rules, exceptions violated them, acting as a behavioural index of flexible learning. We quantified the integrity of white matter tracts across the whole human brain using diffusion-weighted imaging and leveraged correlational tractography to uncover their behavioural relevance. Results: Correlational tractography revealed two distinct white matter networks associated with individual variability in either rule or exception learning. The network supporting exception learning was predominantly subcortical-limbic, comprising the fornix, thalamic radiations, and forceps minor alongside the left frontal-parietal cingulum, a pattern consistent with hippocampal-prefrontal communication and cognitive control over atypical exemplars. Conversely, the network for rule-based items was distinguished by long-range cortico-cortical and cortico-cerebellar pathways, including the right frontal-parietal cingulum, the middle longitudinal fasciculus, and the middle cerebellar peduncle, reflecting the integration of visual features with abstract rule representations and their gradual automatization. Discussion: These findings provide novel evidence that complementary white matter networks support flexible concept formation and offer a neuroanatomical basis for characterizing individual differences in flexible concept learning.