Introduction: The middle temporal gyrus (MTG) is understood to play a role in language-related tasks such as lexical comprehension and semantic cognition. For example, this gyrus is important for understanding visual and auditory messages, and is thought to utilize contextual knowledge to retrieve relevant semantic information required for these tasks. A detailed description of the underlying white matter tracts associated with the MTG could prove useful in refining our understanding of semantic function and its preservation. Through DSI-based fiber tracking validated by gross anatomical dissection as ground truth, we have characterized the underlying white matter connections of the MTG based on their relationships to other well-known structures.
Methods: Diffusion imaging from the Human Connectome Project for 10 healthy adult controls was used for tractography analysis. We evaluated the MTG as a whole based on connectivity with other regions. All tracts were mapped in both hemispheres, and a lateralization index was calculated with resultant tract volumes. Ten postmortem dissections were performed using a modified Klingler technique to demonstrate the location of these tracts.
Results: We identified two major white matter bundles leaving the MTG: the inferior longitudinal fasciculus (ILF) and superior longitudinal fasciculus (SLF). The ILF courses posteriorly from the anterior pole of the MTG to the lingual and cuneal gyri, passing deep to the SLF which courses from the MTG underneath the inferior parietal lobule to parts of the superior, middle and inferior frontal gyri. In addition to long association fibers, a unique linear sequence of u-shaped fibers was identified in the MTG possibly representing a form of visual semantic transfer down the temporal lobe.
Conclusions: The MTG is an important center for semantic processing. Subtle differences in language function following surgery for temporal lobe tumors may be better understood in the context of the fiber-bundle anatomy highlighted by this study.
Patient Care: Precisely how the brain transmits semantic information from the visual system to speech areas remains poorly defined. Our research provides some new detail into the anatomy of ventral semantic transfer and its preservation.
Learning Objectives: By the conclusion of this session, participants should be able to define the key white matter tracts connecting to the middle temporal gyrus and understand the different models of ventral semantic transfer.