Arcuate fasciculus of the brain: location and functions.

This bundle of nerve fibers is associated with Broca's and Wernicke's areas.

Speech is one of the abilities or skills to which most value has traditionally been attached. And although most people use it automatically and even without thinking about what they are saying, the truth is that speaking involves a series of complex processes.

These processes are carried out by different brain areas. One of the main ones, along with Broca's and Wernicke's areas, is the arcuate fasciculus, is the arcuate fasciculus..

Arcuate fasciculus: what is it and where is it located?

We understand by arcuate fasciculus a specific brain region consisting of a set of nerve fibers that connects two of the main areas related to language: Broca's and Wernicke's areas. In this sense, it should be noted that the connection is bidirectional: fibers go from Wernicke's area to Broca's area but also vice versa..

This bundle thus connects frontal and temporal areas, as well as parietal and perisylvian areas. That is to say, it joins motor and sensory areas. These connections are formed by white matter: that is, the arcuate fasciculus is mainly formed by neuronal axons, and neuronal nuclei are not so frequent. They are usually short, arcuate neurons (hence the name).

These fibers can be found in both cerebral hemispheres, although the most relevant one has been found in both hemispheres.although the most relevant to the study is the one of the dominant hemisphere of language (in most people the left one).

Main functions

This small brain region plays a very important role in our behavior, especially with regard to language. Interestingly, although the role of this fasciculus in the dominant hemisphere for language has been largely analyzed, the existing knowledge about its function in the other hemisphere is not fully known. Broadly speaking, we can say that some of the main functions of the arcuate fasciculus are the following.

Sound information

Different studies seem to reflect that the role of the arcuate fasciculus in language is not at the level of meaning. is not at the level of meaning, but only at the level of sounds.. In other words, what is transmitted is not the meaning, which need not have been processed at the conscious level, but the phonemes.

2. Connection between Broca and Wernicke

As mentioned above, the arcuate fasciculus is a set of fibers linking Broca's and Wernicke's areas. That is, it links the main brain areas responsible for language production and comprehension. Although its lesion does not prevent either understanding or producing languageThe arcuate fasciculus is important in linking these two processes.

3. Repetition capacity

Probably one of the most visible functions of this area (given that its lesion prevents it), is the ability to repeat words. That is, the arcuate fasciculus enables us to repeat what another person says to us, something largely linked to theThis is largely linked to the previous point. This aspect makes sense if we think that the fasciculus connects Wernicke's area with Broca's area. That is to say: first we understand what is said to us and then we replicate it.

4. Word learning

Likewise, another of the functions in which the arcuate fasciculus is involved is word learning. Largely linked to its role in repetition capacity, it has been observed through magnetic resonance imaging how those with better verbal learning have a higher level of myelination of the arcuate fasciculus. a higher level of myelination of the arcuate fasciculus.

This implies that the nerve signal will go down the fascicle at a higher speed, and probably a certain link can be found with its association with the ability to repeat the words that are said to us.

5. Prosody, semantics and phoneme-morpheme transformation

It has been observed in several studies that semantics and prosody are also influenced by this brain structure. It also contributes to the process of transforming phonemes (sounds) into morphemes (morphemes). (sounds) into morphemes (already with meaning) even though the information passing through it is primarily phonetic.

6. Musical perception

One of the few functions with which the right arcuate fasciculus has been related is linked to musical perception. It seems that the functioning of the upper part of the arcuate fasciculus of this hemisphere makes us able to capture the different tones of a melody..

7. Writing

It has been shown that the arcuate fasciculus not only influences oral language but also written language, especially in tasks in which it is necessary to move from spoken to written material, such as dictation.

Effects of its lesion

Although the arcuate fasciculus is a relevant element for the human being, it is certain that its lesion does not prevent neither the reception and comprehension of language nor its expression.. However, it can cause great difficulties.

Although comprehension and expression are preserved, their joint action is cut off if there is a lesion in the arcuate fascicle. It has also been seen that the lesion of this brain region causes conduction aphasia, in which it is impossible or very difficult to repeat words. or greatly impairs the ability to repeat words, and the ability to repeat words is. And not only at the oral level: the lesion of the arcuate fasciculus also causes difficulties in performing tasks such as dictation, presenting a certain level of agraphia and sometimes not knowing how to correct misspelled words despite knowing that they are wrong.

Likewise, it has been seen that there may be a link with the perception of tones, being able to generate deafness to them and difficulties in musical perception.

Bibliographical references:

• López Barroso, D.; Catani, M.; Ripollès, P.; Dell'Acqua, F.; Rodríguez Fornells, A.; De Diego Balaguer, R. (2013). Word learning is mediated by the left arcuate fasciculus. Proceedings of the National Academy of Sciences.