Uncinate fasciculus of cerebrum

The uncinate fasciculus of cerebrum is a distinctive hook-shaped, bidirectional long association fibre tract that connects the anterior temporal lobe with orbitofrontal and anterior prefrontal regions of the same cerebral hemisphere. It provides a direct frontotemporal pathway linking anterior temporal cortical regions particularly with the lateral orbitofrontal cortex and frontal pole.

The temporal fibres of uncinate fasciculus arise principally from the anterior temporal cortex, including the temporal pole, uncus, entorhinal and perirhinal cortices and anterior parahippocampal regions. The fibres converge within the anterior temporal stem, pass superiorly through the limen insulae, and traverse the anterior part of the external–extreme capsule region. Here, the uncinate fasciculus lies inferior to the inferior occipitofrontal fasciculus and runs alongside it before the two pathways diverge towards their respective frontal and posterior connections.

Within the frontal lobe, the fibres spread into approximately two components. A larger lateral or ventrolateral component curves towards the lateral orbitofrontal and adjacent frontal opercular/lateral cortex, whereas a smaller medial component continues towards the frontal pole and ventromedial frontal cortex.

Functional correlates

Functionally, the uncinate fasciculus is best regarded as an important pathway for frontotemporal integration rather than as a tract dedicated to a single function. Its bidirectional connections allow information represented within the anterior temporal lobe (including learned associations and person- or object-related information) to interact with orbitofrontal systems concerned with reward, punishment and valuation. It therefore contributes to networks involved in associative learning, memory retrieval, valuation, decision-making and social-emotional behaviour.

The left uncinate fasciculus also contributes to aspects of lexical-semantic retrieval and naming, particularly proper-name retrieval, but it should not be regarded as essential for general language function.

Important distinction

Despite its hook-shaped course, the uncinate fasciculus is a long association tract, not a short U-fibre. It must also be distinguished from the inferior occipitofrontal fasciculus: the uncinate predominantly links the anterior temporal lobe with frontal regions, whereas the inferior occipitofrontal fasciclus provides much longer connections from posterior occipital/parietal regions to the frontal lobe. Their close relationship around the insula and external–extreme capsule can make them difficult to distinguish using some tractographic methods.