Diffusion MRI properties of the human uncinate fasciculus correlate with the ability to learn visual associations.

The uncinate fasciculus (UF) is a cortico-cortico white matter pathway that links the anterior temporal and the orbitofrontal cortex (OFC). In the monkey, transection of the UF causes significant impairments in learning conditional visual-visual associations, while object discrimination remains intact, suggesting an important role for the UF in mediating the learning of complex visual associations. Whether this functional role extends to the human UF has not been tested directly. Here, we used diffusion tensor magnetic resonance imaging (dMRI) and behavioral experiments to examine the relation between learning visual associations and the structural properties of the human UF. In a group of healthy adults, we segmented the UF and the inferior longitudinal fasciculus (ILF) and derived dMRI measures of the structural properties of the two pathways. We also used a behavioral experiment adapted from the monkey studies to characterize the ability of these individuals to learn to associate a person's face with a group of specific scenes (conditional visual-visual association). We then tested whether the variability in the dMRI measures of the two pathways correlated with variability in the ability to rapidly learn the face-place associations. Our study suggests that in the human, the left UF may be important for mediating the rapid learning of conditional visual-visual associations whereas the right UF may play an important role in the immediate retrieval of visual-visual associations. These results provide preliminary evidence suggesting similarities and differences in the functional role of the UF in monkeys compared to humans. The findings presented here contribute to our understanding of the functional role of the UF in humans and the functional neuroanatomy of the brain networks involved in visual cognition.