Aphasias: the main language disorders
One of the reasons why neuropsychology is interesting is that it allows us to see to what extent mental processes that seem to be a single thing are, in reality, the result of many different mechanisms that act simultaneously in the human brain. Prosopagnosia, for example, is proof that a person with the ability to see perfectly can become incapable of recognizing human faces.
Although the vision of something that should be familiar and its recognition seems to have to go hand in hand, an injury in certain areas of the brain can make that illusion vanish, by canceling one of these mechanisms and making the other have to keep working without counting on him.
But this does not happen only with the basic mental processes related to perception, but it is also extended to those more related to more abstract thinking. Aphasias, for example, are an example of how certain facets of language use and proficiency , and not others, can be altered from certain lesions in the brain.
What are aphasias?
Aphasias are a set of language disorders caused by brain damage. Unlike what happens with other kinds of language alterations, such as alexia, an aphasia affects both spoken and written language .
A person with aphasia has altered his ability to use language itself, both in the understanding and in the production of this, although he has no perceptual or motor problem that could prevent him from hearing or seeing well or moving the muscles of his mouth to speak .
What causes aphasia?
The variety of brain injuries that can trigger the onset of aphasia (or several types of aphasia at the same time) are very varied, because the network of neurons that have a role in the production or understanding of language is very distributed .
It is generally considered that aphasias occur when an injury interrupts the flow of information through which images and thoughts are passed on to organized linguistic symbols following the language structure (in a similar way to when we notice that we have a word "on the tip of the tongue") or when this brain damage prevents the words heard or read from being transformed into images and thoughts.
However, this is still the result of discussion, since it is not clear to what extent our brain distinguishes between thoughts formulated as part of language and thoughts that exist independently of the languages that are mastered . On the other hand, the concept "aphasia" is quite abstract. What many patients with language disorders present are, rather, types of aphasias.
Types of aphasias
From a practical point of view it is not as useful to talk about the causes of aphasia in general as it is about the different types of aphasia, since this lets you know what happens to each particular patient . In addition, the existence of these different kinds of aphasias allows us to see that in language it is really a puzzle of different mental processes that normally we would not think of considering separately.
Then you can read what these types of aphasias are .
People with Broca's aphasia they have more difficulties in the production of language than in their comprehension. They have a hard time writing and speaking, they take a long time to choose the words they want to say and they also have trouble pronouncing and modulate the tone of voice. The symptoms of this type of aphasia can be detected even by someone who does not understand the patient's language.
Although they have less difficulty understanding texts or oral language compared to their ability to speak and write, people with Broca's aphasia will be unable to literally repeat the phrases or words they hear , regardless of whether they understand them or not.
An example of a fictional character with symptoms similar to the classic picture of Broca's aphasia is Hodor , from the series Game of Thrones and the books Song of Ice and Fire: although he seems to understand what is being said to him, his ability to speak is almost completely nullified.
Unlike what happens in the previous type of aphasia, in Wernicke's speech is fluent and it is not difficult to speak with a normal rhythm or even very quickly, maintaining correct pronunciation and intonation .
However, usually the phrases or words produced by a person with Wernicke's aphasia they are not well constructed, since words are often replaced by others belonging to the same semantic field (for example, replacing "oven" with "washing machine"), some phonemes are exchanged for others (change "cat" to "gado") or sentences are built with great syntactic failures in which nothing can be understood because there is no adequate structure and verbs have been replaced by adverbs, nouns by articles, etc.
Further, in this type of aphasia the comprehension of the oral language and the writing is quite altered , as well as the ability to repeat words.
If in Broca's and Wernicke's aphasias the injury affects the areas related, respectively, with the production of language and the organization of language to form units with meaning, in the driving aphasia Brain damage affects the networks of neurons that connect these two nuclei of the brain.
That is why a patient with this type of aphasia will have a fluent speech and his ability to understand the language will be preserved in a relatively good state, but you can not literally repeat the words or phrases you hear and see written , since in order to do that they must be intact the circuits that lead from the part of the brain in which the word or phrase is recognized as a whole with meaning to that in which this information is "translated" into speech instructions or writing.
In addition, in this type of aphasia the phrases that are produced also tend to present undue substitutions of phonemes and words.
Another type of aphasia is global aphasia . Consists in a generalized alteration of the language that seriously affects both the production and the understanding of the language . In general, people with this syndrome can not repeat words or phrases, and in some cases will only be able to say one or a few syllables or words that will repeat regardless of the context.
The transcortical aphasias they are characterized by maintaining the ability to repeat phrases and words, something that did not happen in the four types of previous aphasias.
Transcortical motor aphasia
In this syndrome there are symptoms similar to those of Broca's aphasia, with non-fluid speech and the ability to understand the most preserved language, but adding the possibility of repeating the phrases you hear or read, no matter how long they are . That is to say, that someone with transcortical motor aphasia is not able to speak spontaneously, but can repeat anything.
Transcortical sensory aphasia
It looks like a version of Wernicke's aphasia in which you can repeat what you hear, but not what you read. Further, Sometimes all kinds of syllables or words that have been heard are repeated involuntarily , phenomenon that is known as ecolalia.
Mixed transcortical aphasia
This type of aphasia is similar to a mild version of the global aphasia in which the ability to repeat is retained, even if what is said is not understood . Echolalia is also common among the typical symptoms of this kind of language alteration.
Unlike what happens with the other types of aphasias, in the anomic aphasia both the production and the understanding of the language can be almost normal, and its main symptom is anomie , that is, the difficulty in finding the right words to say something. People with anomic aphasia tend to use many generic terms like "thing", "that", etc. From time to time these difficulties lead them to use circumlocutions, to try to explain themselves again using alternative phrases or to lengthen a lot what is being said to try to accumulate the details and clues about what is meant.
The language is more complicated than it seems
It is not always easy to identify the types of aphasias that some patients present, since the symptoms can vary a lot and be more or less serious , but in all of them (except in the global) it is clear that behind the use of language there are many parts of the brain more or less specialized in a task and coordinating with each other so that everything works as it should.
Therefore, certain capacities can be lost while others, closely related to the former, are preserved.