Uncinate fasciculus: characteristics, parts and functions in the brain.

Summary of the characteristics of the uncinate fasciculus, a bundle of nerve fibers.

The uncinate fasciculus is a brain tract that is related to the limbic system, although the exact function of the uncinate fasciculus is still unknown.The exact function of the uncinate fasciculus is still unknown.

What is known is that if it is damaged it can cause several psychiatric problems and memory problems, as well as personality changes.

It is one of the structures that takes the longest time to develop fully and, below, we will find out more about its anatomical trajectory and what symptoms are related to its lesion.

What is the uncinate fasciculus?

The uncinate fasciculus, classically called the frontotemporal fasciculus, is a tract of white matter association 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 is named for its hook-like shape 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 has been shown that its involvement It is not known exactly what its function is, but it has been shown that its involvement would be behind several psychiatric conditions, such as mood disorders.such as mood disorders, memory lapses and disorders such as schizophrenia. It is known to be one of the last tracts to mature in the human brain, with full maturity being achieved in late young adulthood.

Pathway 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 frontal lobe.It passes through the M1 portion of the middle cerebral artery at 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 frontoorbital cortex. The fibers also connect to the cortical nuclei of the amygdala and hippocampus with the right gyrus and septal area.

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

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

Within the uncinate fasciculus we can distinguish two types of fibers, there are dorsal or lateral fibers, which occupy the outermost part of the tract and are easier to dissect and separate, and other medial or ventral fibers, which are more compact and united. The dorsolateral fibers link to the pole 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 right gyrus and the subcallosal area.

Near the uncinate fasciculus are white matter capsules or strata. separating different nuclear formations of 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 course, and interconnect various parts of the cortex with each other. In some specific points of the segments some fibers of the uncinate fasciculus can lodge inside these capsules.

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

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 fasciculus allows storing mnemonic representations in the temporal lobe, as well as guiding decision making in the frontal lobe. in the frontal lobe.

By means of diffusion tensor imaging, it has been found that this structure has a higher activity on the left side than on the right. This has been related to language specialization in 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, so it is doubtful that it has any relationship with language.

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

Development

The uncinate fasciculus is one of the regions of the brain that takes the longest to complete its development.reaching full maturity at the age of 30 years. Problems in name recall, reward learning and impulsive decision making have developed with 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 prematurely born. In 10-year-old children with socioemotional depravation the left uncinate fasciculus has been observed fractional anisotropy. The reduced level of the child's symptoms compared to that of another child, which is related to behavioral, cognitive and social-emotional problems.

Clinical Significance

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

It has also been linked to psychopathy and violent behavior, as seen in 2009 research linking damage to the uncinate fasciculus with higher scores on the Psychopathy Checklist.

One of the most famous cases of brain damage in the history of neurology is Phineas Gage.. This man was a railroad track worker who had an accident in which a steel rod pierced his left frontal lobe. Probably, in this accident his uncinate fasciculus was destroyed, along with other regions. This caused him to suffer personality and behavioral changes, becoming impulsive, making bad decisions and not following social norms.

Bibliographical references:

• Karnath, H.O.; Hartje, W. & Ziegler, W. (2006). Kognitive Neurology. Thieme, Stuttgart, ISBN 3-13-136521-8, S. 58.
• Förstl, 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 frontooccipital fasciculus as dissemination pathways of limbic gliomas. Neuroanatomy, 39-43.