Complementary white matter networks support flexible concept learning

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.

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.

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.

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.