Uncinate fasciculus: characteristics, parts and functions in the brain

The uncinate fasciculus is a cerebral tract that is related to the limbic system., despite the fact that to this day it is unknown exactly what function it has.

What is known is that if it is damaged it can cause various problems at the psychiatric level and memory problems, as well as personality changes.

It is one of the structures that take the longest to fully develop and, Next, we will discover more in depth what is its anatomical trajectory and what symptoms are related with his injury.

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What is the uncinate fasciculus?

The uncinate tract, classically called the frontotemporal tract, is a white matter association tract in the human brain, which connects different parts of the limbic system such as the parahippocampus, the amygdala in the temporal lobe, portions of the frontal lobe, and the orbitofrontal cortex. It gets its name from the hook shape it has, and should not be confused with the uncinate fasciculus of the cerebellum or Russell's tract.

It is not known exactly what its function is, but it is it has been seen that its affectation would be behind several psychiatric conditionssuch as mood disorders, memory lapses and disorders such as schizophrenia. It is known to be one of the last to mature tracts of the human brain, reaching full maturity in late young adulthood.

tour and parts

The uncinate fasciculus extends from the basal aspect of the frontal lobe to the lateral aspect of the temporal pole, passing through the M1 portion of the middle cerebral artery in the limen of the insula. This fascicle is made up of fibers that join at the end of the superior, middle, and inferior temporal gyri with the fronto-orbital cortex. The fibers also connect with the cortical nuclei of the amygdala and hippocampus with the rectus gyrus and the septal area.

The uncinate fasciculus It can be divided into three segments: temporal, insular, and frontal.. The temporal segment arises from the amygdala nuclei, specifically in areas 28, 34 and 36, the perrinal area of ​​the mesocortex (area 35) and from the anterior part of the three temporal gyri (areas 20 and 38), connecting with the frontal segment in the area of ​​the subcallosal gyrus (area 25), the gyrus rectus (area 11), and the posterior orbital cortex at its areas 47, 13 and 14

the fascicle It is a solid tract of fibers between 3 and 7 mm wide and between 2 and 5 mm high., which travels along the lateral part of the extreme and external capsule on the ventral circumference of the putamen towards the retroorbital cortex. The frontal part is oriented horizontally in the straight gyrus, retro-orbital cortex, and the subcallosal area.

Within the uncinate fascicle we can distinguish two types of fibers, some being dorsal or lateral, which occupy the upper part. outermost part of the tract and which are easier to dissect and separate, and other medial or ventral fibers, which are more compact and united. The dorsolateral fibers attach to the poles of the first and second temporal gyri in the lateral retroorbital cortex. Ventromedial fibers connect the uncus, the cortical nuclei of the amygdala and the tip of the third temporal gyrus with the gyrus rectus and the subcallosal area.

Close to the uncinate fasciculus are the capsules or layers of white matter. that separate different nuclear formations from the gray. The claustrum is separated from the striatum by the external capsule, and is laterally related to the cortex of the insula, which are separated by the extreme capsule. The fibers that circulate through these two capsules have a longitudinal route, and interconnect various parts of the cortex with each other. At some specific points of the segments, some fibers of the uncinate fasciculus can lodge inside these capsules.

The medial uncinate fibers filter through the external capsule, while the more lateral filaments pass through the extreme capsule. The most lateral part of the fascicle forms part of the extreme capsule and the most medial part of the external capsule. The claustrum is found as if it were a sheet of gray matter between the two capsules.

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Function

The exact function of the uncinate fasciculus is not yet known, although it is traditionally considered part of the limbic system. It has been proposed that this fascicle makes it possible to store mnemonic representations in the temporal lobe, in addition to guiding decision making. in it frontal lobe.

Using diffusion tensor imaging, this structure has been found to be more active on the left side than on the right. This has been related to the specialization in the language of the left hemisphere. In any case, the use of electrical stimulation in the brain, specifically above the uncinate fasciculus, does not hinder the ability to communicate, which is why it is doubted that it has any relationship with the language.

What is believed is that may have a role in some types of learning and memory, although not in all. It seems to be especially involved in stimulus-reward learning. It has also been related to name-object/person learning, since lesions in this region imply deficits in the memory of names.

Development

The uncinate fasciculus It is one of the regions of the brain that takes the longest to complete its development, reaching its full maturity at 30 years. Problems in remembering names, learning for rewards and having impulsive decision making have developed with having a poorly developed uncinate fasciculus.

It is a very vulnerable region. Abnormalities in the left anterior uncinate fasciculus have been found in 12-year-old boys who were premature. Fractional anisotropy has been observed in 10-year-old children with socio-emotional deprivation of the left uncinate fascicle. reduced compared to that of another child, which is related to behavioral, cognitive and socio-emotional problems.

clinical significance

Malformations and poor development of the uncinate tract have been linked to various neuropsychiatric disorders, including social anxiety, depression and schizophrenia. It has also been linked to dementias, such as Alzheimer disease, semantic dementia and temporal lobe epilepsy.

It has also been linked to psychopathy and violent behavior, something seen in research from the 2009, in which damage to the uncinate fascicle was associated with higher scores in the Psychopathy Check list.

One of the most famous cases of brain damage in the history of neurology we have it in Phineas Gage. This man was a railroad worker, who had an accident in which a steel rod pierced his left frontal lobe. Probably, in this accident his uncinate fascicle was destroyed, along with other regions. This caused him to suffer personality and behavior changes, becoming an impulsive person, who made bad decisions and did not follow social norms.

Bibliographic references:

• Karnath, H.O.; Hartje, W. & Ziegler, W. (2006). Kognitive Neurology. Thieme, Stuttgart, ISBN 3-13-136521-8, S. 58.
• Forstl, H.; Hautzinger, M.; Roth, G. (2006.). Neurobiologie psychischer Störungen. Springer: Berlin. ISBN 3-540-25694-6.
• Piquer-Belloch, J.; Llacer-Ortega, J.L. & Riesgo-Suárez, P. (2013). Anatomy of the uncinate and inferior fronto-occipital fasciculus as routes of dissemination of limbic gliomas. Neuroanatomy, 39-43.