Lateral surface of left cerebral hemisphere. Some of the major association tracts are depicted. Uncinate fasciculus is at lower left, in red.
Human brain with operculum removed. A part of uncinate fasciculus is visible (shown in yellow)
|Anatomical terms of neuroanatomy|
The uncinate fasciculus is a white matter association tract in the human brain that connects parts of the limbic system such as the hippocampus and amygdala in the temporal lobe with frontal ones such as the orbitofrontal cortex. Its function is unknown though it is affected in several psychiatric conditions. It is the last white matter tract to mature in the human brain.
The uncinate fasciculus is a hook-shaped bundle that links the anterior portions of the temporal lobe with the inferior frontal gyrus and the lower surfaces of the frontal lobe. It does this by arising lateral to the amygdala and hippocampus in the temporal lobe curving in an upward pathway behind the external capsule inward of the insular cortex and continuing up into the posterior part of the orbital gyrus.
The average length of the uncinate fasciculus is 45 mm with a range 40–49 mm. Its volume in adults is 1425.9±138.6 mm3, being slightly larger in men, at 1504.3±150.4, than women 1378.5±107.4.
It has three parts: a ventral or frontal extension, an intermediary segment called the isthmus or insular segment and a temporal or dorsal segment.
Diffusion tensor imaging, a reconstruction model available from a diffusion MRI scan, shows a greater fractional anisotropy on the left side than on the right. The difference in this measure of anisotropy has been linked to the left hemispheric specialization for language. However, the use of electrical brain stimulation upon it fails to disrupt language, suggesting it might not be involved in language, though it is possible that this disruption failed to happen because it was functionally compensated by alternative pathways.
The capacity for autonoetic self-awareness that is re-experiencing previous events as part of one's past as a continuous entity across time has been linked to the right uncinate fasciculus as has proficiency in auditory-verbal memory and declarative memory to the integrity of the left uncinate fasciculus.
The uncinate fasciculus has the longest period of development in terms of fractional anisotropy as it alone amongst the major white fibre tracks continues to develop beyond the age of 30.
It seems to be developmentally vulnerable. In 12-year-old males that were preterm, abnormalities measured by fractional anisotropy in the left anterior uncinate correlated with verbal IQ, full-scale IQ, and Peabody Picture Vocabulary Test-Revised scores. In 10-year-old children who have suffered socioemotional deprivation, the left uncinate fasciculus shows reduced fractional anisotropy compared to that in other children, and this might underlie their cognitive, socioemotional, and behavioral difficulties.
Abnormalities within the fiber bundles of the uncinate fasciculus associate with social anxiety, Alzheimer's disease, bipolar disorder, and depression in the elderly that had previously been present in adolescence or early adulthood.
Such abnormalities also link to schizophrenia. In those with schizotypal personality disorder, reduced fractional anisotropy in the right uncinate fasciculus associates personality traits and clinical symptoms of ideas of reference, suspiciousness, restricted affect, reduced extraversion and social anxiety, while those on the left side associate with general intelligence, verbal and visual memory, and executive performance. The greater left than right fractional anisotropy of the uncinate fasciculus is missing in those with schizophrenia.
Phineas Gage ( a railroad worker who had an iron bar go through his left frontal lobe) had damage done to his uncinate fasciculus. After the accident, his intellect was untouched, but his personality transformed. He lost all sense of morality and concern for others.
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|Wikimedia Commons has media related to Uncinate fasciculus.|
- Atlas image: n1a5p6 at the University of Michigan Health System - "Dissection of the Left Hemisphere"