Speech is one of the most traditionally valued capacities or skills. 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 Broca and Wernicke’s areas, is the arched fascicle .

Arched fascicle: what is it and where is it located?

By arched fascicle we understand a specific brain region that consists of a set of nerve fibers linking 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: the fibers go from the Wernicke area to Broca’s area but also vice versa .

This beam thus connects frontal and temporal areas, as well as parietal and perisylvanian areas. In other words, it brings together motor and sensory areas. These connections are formed by white substance: that is, the arched fascicle is mainly formed by axons of neurons, not being so frequent to find neuronal nuclei. They are usually short, arched neurons (hence their name).

We can find these fibers in both brain hemispheres , although the most relevant one 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 when it comes to language. Interestingly, while the role of this fascicle 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 arched fascicle are the following.

1. Sound information

Different studies seem to reflect that the role of the arched fascicle in language is not at the level of meaning, but only at the level of sounds . That is, what is transmitted is not the meaning, which does not have to be processed at a conscious level, but the phonemes.

2. Connection between Broca and Wernicke

As mentioned above, the arched fascicle is a set of fibers linking the Broca and Wernicke areas. That is, it joins the main brain areas in charge of language production and comprehension. Although its lesion does not prevent either understanding or producing language , the arched fascicle has its importance in linking these two processes.

3. The ability to repeat

Probably one of the most visible functions of this area (since its lesion prevents it), is the ability to repeat words. That is, the arched fascicle 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 the Wernicke area with the Drill. That is: first we understand what we are told and then we replicate it.

4. Word learning

Likewise, another function in which the arched fascicle is involved is word learning. Largely linked to its role in the capacity of repetition, it has been observed through magnetic resonance how those people who have better verbal learning possess a higher level of myelinization of the arched fascicle.

This implies that the nervous signal will go down faster through the fascicle, and probably some link can be found with its association with the ability to repeat the words we are told.

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 (already with meaning) despite the fact that the information passing through it is fundamentally phonetic.

6. Musical perception

One of the few functions with which the right-hand arched fascicle has been related is linked to musical perception. It seems that the function of the upper part of the arched fascicle of that hemisphere makes us capable of capturing the different tones of a melody .

7. Scripture

It has been seen that the arched fascicle influences not only oral language but also writing, especially in tasks where it is necessary to move from spoken to written material such as dictation.

Effects of your injury

Being the arched fascicle a relevant element for the human being, the truth is that its injury does not prevent neither the reception and understanding of the language nor its expression . However, it can generate great difficulties.

Although understanding and expression are preserved, their joint performance is cut off if there is an injury to the arched fascicle. It has also been seen that the lesion of this brain region causes conduction aphasia, in which makes it impossible or very difficult to repeat words . And not only on an oral level: the lesion of the arched fascicle also causes difficulties in carrying out tasks such as dictation, presenting a certain level of agraphy and sometimes not knowing how to correct badly written words despite knowing they are wrong.

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

Bibliographic 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.