Distinct contributions of hippocampal pathways in learning regularities and exceptions revealed by functional footprints
Fundamental aspects of learning are theorized to be supported by hippocampal pathways: monosynaptic pathway (MSP) extracts regularities whereas trisynaptic pathway (TSP) rapidly encodes exceptional items. Yet, the empirical evidence for the dynamic involvement of MSP and TSP in learning remains elusive. We leveraged diffusion-weighted imaging to estimate the end points of MSP- and TSP-related white matter structures (i.e., footprints) within hippocampal subfields and entorhinal cortex. We then measured the activation of pathway-specific footprints with functional magnetic resonance imaging while participants learned novel concepts defined by regularities and exceptions. The functional footprint method revealed links between MSP-related footprint activation and regularity encoding early in learning, and TSP-related footprint activation and exception encoding late in learning. These findings provide novel evidence that learning concept regularities and exceptions is distinctly supported by hippocampal pathways. Pathway footprint approach provides insights into the functional dynamics of the human hippocampus, translating theoretical and computational work into empirically testable questions in humans.