Auditory cortex: characteristics and functions of this region of the brain

The cortex of the brain includes areas specialized in specific tasks. This is the case, for example, of the auditory cortex.

We will dedicate the following lines to better understand the function of this part of the brain, its characteristics and most important regions. Likewise, we will see with what other parts of the nervous system and the human organism it is connected to achieve its functions.

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

What is the auditory cortex of the brain? Location and features

The auditory cortex of the brain is a part of this organ in charge of processing all the information that we obtain through the auditory system, that is, the sounds that the ears pick up. Its location is in the temporal lobe and within this area we can find it in the so-called Heschl area, formed by the transverse convolutions.

Another way to find this region is by going to the map of the ancient Brodmann areas, as the auditory cortex of the brain would be occupying parts 41, 42 and part of the 22

, within this map. This region of the cerebral cortex can be found both in the brain of humans and in that of a large number of vertebrate animal species.

Parts and structure

Regarding the structure, the auditory cortex of the brain can be subdivided into primary (A1), secondary (A2) and tertiary (A3) auditory cerebral cortex. The primary has a thickness of approximately 3 millimeters. At the macrostructural level, we have already seen that it is located in the Heschl area, occupying half of that entire area.

If we go to the microstructure, we can find several ways to study this part of the brain. For example, at the level of neuronal arrangement or cytoarchitecture, part A1 would make up part of the so-called koniocortex, a grouping of neurons with a granular appearance. The auditory cortex of the A1 brain has several layers, showing greater density in numbers II and IV. As for III, it is characterized by the existence of pyramidal cells.

If we focus on the chemical composition, or chemoarchitecture, we will discover that the A1 zone is largely composed of CO, cytochrome oxidase, and AChE, acetylcholinesterase. By last, the distribution of myelin, or myeloarchitecture, denotes large concentrations of this substance in the primary part, precisely where more sensory projections occur.

Precisely because of this great myelination, the auditory cortex of the primary brain type (A1) can be easily observed by magnetic resonance imaging.

In the case of primates, and more specifically in humans, We can divide this zone, from the most central to the most peripheral, as the nucleus, inner belt and outer belt. The nucleus would house section A1 and also the rostral or R part. The inner belt would house the auditory cortex of the secondary brain, that is, the A2 zone. Finally, the outer strip is the place where we would find the tertiary section, or A3.

The auditory cortex of the brain is part of the so-called neocortex. This area is characterized by the need for a certain stimulation during development to be able to perform all functions correctly. In this sense, for the auditory cortex to perform its tasks in a normal way, it will have been necessary that has been exposed to different auditory frequencies in the early stages of the child's life organism.

Functions of the auditory cortex of the brain

The function of the auditory cortex of the brain, as is evident, is to process the data captured by the auditory system. If this part of the brain did not do this work, no matter how structurally the ears functioned correctly, it would not we would have a way of being able to use the sense of hearing, since there would be no reception and interpretation of the sounds captured by said system.

For this reason, some brain injuries due to trauma, disease, stroke or tumors that damage this area, they can cause deafness at a functional level, regardless of whether the ears are not affected. However, although the sounds cannot be interpreted, these subjects still show reflex behaviors to some of them.

The explanation for this phenomenon is due to the fact that, before reaching the auditory cortex of the brain, there is a first information processing that takes place in the brainstem and midbrain.

What's more, each group of neurons in the auditory cortex of the brain is specialized in processing sounds belonging to a certain frequency. In this way, it can be observed that, starting from one end, the neurons that process low frequencies (from 2 Hz) and As we advance towards the other end of this cortex, the nerve cells process the highest frequencies, until we reach those of 128 Hz.

Due to this phenomenon, there are frequency maps or tonotopic maps that indicate exactly which area of ​​the auditory cortex of the brain is dedicated to specific sound frequencies. This region of the brain, by interpreting the data obtained by the ear, is able to locate where sounds come from and also identify and classify them.

It is not yet fully understood how this part of the brain is capable of performing this activity with such precision, since Identifying the continuum of a specific sound, ignoring the rest of the noise that is constantly perceived, is something extremely complex. One theory is that the key is in the spatial location of the sound source, but when it varies constantly does not pose a problem for the auditory cortex of the brain, so there must be another Explanation.

In turn, the auditory cortex of the brain is able to discern between the different keys, the harmony and the timing of the notes. This facet is very well observed in terms of musical interpretation and how we are able to distinguish each sound, coming from a whole range of instruments, and interpret them all together.

We have already seen that the auditory cortex of the brain was divided into three parts (primary, secondary and tertiary) and which is also neuronally structured by the type of sound frequencies that they manage. What's more, zone A1 also has connections with other regions of the nervous system such as the thalamus, and more specifically with the area of ​​the medial geniculate nucleus.

It is believed that this part is responsible for the interpretation of the volume of the sound and also of the perceived tones.

• You may be interested in: "Temporal lobe: structure and functions"

Types of dysfunctions in the auditory cortex

There are different pathologies that can be caused by injuries or abnormalities in the auditory cortex of the brain.

We have already mentioned cortical-type deafness, which occurs when the A1 zone is damaged and therefore the individual cannot process the sounds that their ears are hearing correctly.

If the lesions, on the contrary, are affecting the secondary or tertiary area, there are other pathologies that the subject can develop. For example, if the damaged area is in the right hemisphere, this person could have trouble recognizing the pitch of sounds, known as amusia. It could be that you are having difficulty getting the sentences right. In this case, the condition would be called dysprosodia.

It could even be affecting other sensory regions, for example those that have to do with visual memory. In the event that the injury affected the left hemisphere, there are other possibilities that we find. The best known are the aphasia, which have to do with difficulties understanding or using language. One of them is Wernicke's, which prevents understanding and repeating the words he is hearing.

Another common aphasia is anomic, in which the person experiencing it has trouble remembering the name of an item.. There could also be another aphasia known as transcortical sensory, which also affects language understanding. The last of the possible aphasias is conduction of the acoustic and amnesic type, which would cause problems to repeat a sequence of words.

Equally, with lesions in the auditory cortex of the brain of the left hemisphere you can also suffer from amnesia for verbal elements, which would also be making it difficult for the person to speak. The amusia that we saw in the other hemisphere can also occur here, also related to the auditory agnosia, the inability to process stimuli received through the ear, in this case.

But it may happen that the injury or disease has affected the auditory cortex of the brain of the two hemispheres of the brain, which would mean a bilateral ailment. In this type we can find that auditory agnosia we were talking about and also verbal deafness, that is, being unable to process the words that the ears are hearing.

Bibliographic references:

• Delahay, F., Regulés, S. (2006). The brain and music. UNAM Science Disclosure Magazine.
• Jara, N., Délano, P.H. (2014). Advances in auditory cortex. Journal of otorhinolaryngology and neck surgery.
• Izquierdo, M.A., Oliver, D.L., Malmierca, M.S. (2009). Mechanisms of plasticity (functional and activity-dependent) in the adult and developing auditory brain. Journal of Neurology.
• Terreros, G., Wipe, B., León, A., Délano, P.H. (2013). From the auditory cortex to the cochlea: Progress in the auditory efferent system. Journal of otorhinolaryngology and head and neck surgery.