Where is the uncinate fasciculus, and what does it join?
The uncinate fasciculus is a hook-shaped bundle of nerve fibres joining the front of the temporal lobe (the temporal pole, the front of the parahippocampal gyrus and the amygdala) to the underside of the frontal lobe, mainly the orbitofrontal cortex. [1][2]
A bundle has no shape of its own in this atlas; lit: the two parts it joins.
The 3D brain needs JavaScript. The legend below still names the two parts the uncinate fasciculus joins.
The brain starts seen from the left, a little from below and the front, so the orbitofrontal cortex on the underside of the frontal lobe and the front of the temporal lobe both show. One end is lit in blue (the orbitofrontal cortex), the other in orange (the temporal lobe and the amygdala); the bundle runs between them. Drag to turn, pinch or scroll to zoom; tap a lit part to name it.
The bundle itself is not drawn: BodyParts3D has no shape for any fasciculus, nor for the temporal pole, so the whole temporal lobe is lit with the amygdala inside it, on both sides; the bundle ends only in the front of the lobe. The hook of fibres between the two ends, behind the insula, is not lit. [3][1]
The two ends: which colour is which
Frontal end: the orbitofrontal cortex, lit in blue: the orbitofrontal cortex, on both sides of the brain.
In front, it ends in the lower surfaces of the frontal lobe: the lateral orbitofrontal cortex and Brodmann area 10 at the frontal pole, with fibres also reaching the inferior frontal gyrus. [2][1]
Temporal end: the front of the temporal lobe, lit in orange: the temporal lobe and the amygdala, on both sides of the brain.
Behind, it arises in the front of the temporal lobe and the amygdala: the temporal pole and the front of the parahippocampal gyrus. It does not appear to have cell bodies in the hippocampus proper. [1]
The bundle runs between the blue and the orange parts; its fibres are not drawn.
From the temporal lobe it curves upward behind the external capsule, inward of the insula, and on into the back of the orbital gyrus: the hook its name describes. [1]
It has three parts: a frontal (ventral) extension, a middle stretch called the isthmus or insular segment, and a temporal (dorsal) segment. [1]
It averages about 45 mm long (range 40–49 mm), with a volume of about 1,426 mm³ in adults, a little larger on average in men than in women. [1]
Signals run both ways along it. One proposal is that it lets associations stored in the temporal lobe, such as a person’s name, face and voice, guide decisions in the orbitofrontal cortex, and lets the reward history kept there reshape those memories. [2][1]
Its exact job is not settled. Studies tie it to some kinds of learning, such as pairing a name with a face, and to retrieving the meaning of words, but not to all learning and memory. [1][2]
It is one of the last white-matter tracts to mature: by one diffusion-imaging measure it alone among the major tracts keeps developing until about age 30. [1]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); it has no shape for any fibre bundle, so a bundle is shown by the two parts it joins.