Arcuate fasciculus of the brain: location and functions

Speech is one of the skills or abilities that has traditionally been given the most value. 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, together with the areas of Broca and Wernicke, is the arcuate fasciculus.

• Related article: "Parts of the human brain (and functions)"

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

We understand by arcuate fascicle to a specific brain region that consists of a set of nerve fibers that unites two of the main areas related to language: the areas Broca's and Wernicke's. In this sense, it should be noted that the connection is bidirectional: fibers run 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, it combines motor areas and sensory areas. These connections are made up of white matter: that is, the arcuate fasciculus is made up mainly of neuron axons, and it is not so frequent to find neuronal nuclei. They are usually short neurons in an arcuate shape (hence their name).

We can find these fibers in both cerebral hemispheres, although the one that has been most relevant to the study is that of the dominant hemisphere of language (in most people the left).

Principal functions

This small brain region plays a very important role in our behavior, especially when it comes to language. Interestingly, while the role of this fascicle in the dominant hemisphere has been extensively discussed for language, existing knowledge about its function in the other hemisphere is not fully acquaintance. Broadly speaking, we can say that some of the main functions of the arcuate fasciculus are the following.

1. Sound Information

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

2. Connection between Broca and Wernicke

As we have previously commented, the arcuate fasciculus is a group of fibers that unite Broca's and Wernicke's areas. That is, it unites the main brain areas responsible for the production and comprehension of language. Yes ok his lesion does not prevent him from understanding or producing language, the arcuate fascicle is important when linking these two processes.

3. repeatability

Probably one of the most visible functions of this area (since his injury prevents it), is the ability to repeat words. That is, the arcuate fasciculus allows us to be able to repeat what another person tells us, something largely linked to the previous point. This aspect makes sense if we think that the fascicle connects Wernicke's area with Broca's. That is to say:: first we understand what we are told and then we replicate it.

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4. word learning

Likewise, another of the functions in which the arcuate fasciculus is involved is in learning words. Largely linked to its role in repeatability, it has been observed through magnetic resonance imaging how Those people who have a better verbal learning possess 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 can Some 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 various studies that semantics and prosody are also influenced by this brain structure. It also contributes to the process of transforming phonemes (sounds) into morphemes (already with meaning) despite the fact that the information that passes through it is fundamentally phonetic.

6. music perception

One of the few functions with which the right arcuate fasciculus has been linked is linked to musical perception. And it seems that the operation of the upper part of the arcuate fascicle of said hemisphere makes us capable of capturing the different tones of a melody.

7. Writing

It has been seen that the arcuate fascicle influences not only oral language but also written language, especially in tasks in which it is necessary to go from spoken to written material as in dictates.

Effects of your injury

Since the arcuate fascicle is a relevant element for the human being, the truth is that his lesion does not impede the reception and comprehension of the language or its expression. However, it can cause great difficulties.

And it is that although comprehension and expression are preserved, their joint performance is cut off if there is a lesion in the arcuate fasciculus. It has also been seen that damage to this brain region causes conduction aphasia, in which makes it impossible or greatly hinders the ability to repeat words. And not only at the oral level: the lesion of the arcuate fasciculus also causes difficulties in carrying out 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, which can generate deafness to them and difficulties in musical perception.

Bibliographic references:

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