Ventral temporal-frontal pathways in the human brain based on diffusion MRI tractography.

In the primate brain, two ventral fiber pathways connect the temporal cortex with the frontal cortex: the Uncinate Fasciculus (UF) and the Temporal-Frontal extreme capsule Fasciculus (TFexcF). The definition and reconstruction of these pathways in the human brain have been inconsistent between research groups and have led to conflicting findings about their functional roles. Here, we define the UF and TFexcF in the human brain based on a review of the temporal-frontal connections demonstrated in the macaque monkey via invasive tracer studies and a novel protocol for reconstructing them in the human brain using diffusion-weighted Magnetic Resonance Imaging (dMRI) tractography. A key advantage of the present protocol is the reconstruction of the tracts based on anatomically defined cortical terminations which would allow interpretation of their functional role given the cortical areas that they interconnect. The UF provides the interaction between orbitofrontal cortex and the anterior-medial temporal region involved in emotional processing and information integration in memory. The dorsal TFexcF enables the online monitoring of information within working memory and the attentional allocation of the highly processed visual, auditory and multisensory information in the anterior-to-middle temporal cortex. Finally, the ventral TFexcF enables the selective retrieval of highly processed visual, auditory and multisensory information via interaction of the ventrolateral prefrontal cortex with the anterior-to-middle temporal cortex.