One of the most characteristic disorders of brain damage is aphasia, which is defined as a impaired ability to understand and / or produce spoken and written language. There is a special type of aphasia which is characterized by the maintenance of the ability to repeat the words heard; one is transcortical aphasias.
In this article we will describe the main characteristics of the three types of transcortical aphasia: Sensory, motor and mixed. By way of introduction, we will briefly explain the general characteristics of aphasias, in particular transcortical ones.
What is transcortical aphasia?
Aphasias are language disorders that appear as a result of injury in speech-related regions of the left hemisphere of the brain, As well as with reading and writing. However, in some people the language is more evenly distributed between the two hemispheres, as is the case with leftists, and the left is not the dominant language.
The most common causes of aphasia are ischemic stroke, head trauma, and neurodegenerative diseases, including dementia.
Against the background of aphasia the term “transcortical” refers to the occurrence of damage to various lobes of the brain that isolate certain neural pathways and structures related to language. The function of these regions is preserved, which explains the symptomatic peculiarities of these aphasias.
The signs of transcortical aphasias vary considerably depending on the type we are referring to (sensory, motor or mixed). However, a common characteristic of all three classes of transcortical aphasia is the maintenance of the ability to repeat words or phrases that have been spoken by other people.
This characteristic distinguishes transcortical aphasia from other variants of this disorder, in particular Broca or motor aphasia, Wernicke or sensory aphasia, conduction aphasia, and global or total aphasia. Beyond that, the usual signs of transcortical aphasias are similar to those of others.
Types of transcortical aphasia
Three types of transcortical aphasia have been distinguished on the basis of the relative predominance of symptoms and signs related to the understanding and production of language.
Thus, we find a sensory, motor and mixed transcortical aphasia, in which both classes of impairment are present to a severe degree.
Sensory transcortical aphasia it is characterized by poor understanding of the languageWhether in speaking or reading, as well as in maintaining verbal fluency. These signs are very similar to those of Wernicke’s aphasia, although in this the repetition is impaired.
In Wernicke’s aphasia and in the transcortical sense, the articulation of phonemes is correct, although speech tends to be full of meaningless terms (neologisms) as well as unnecessary syllables and words (paraphrases) that have a meaning for verbal production.
This kind of aphasia is associated with lesions at the bottom of the junction between the temporal, parietal and occipital lobes, Which correspond to zones 37 and 39 of the classification made by Brodmann. In this part of the brain we find Silvio’s cleft or lateral sulcus of the brain, one of its most prominent folds.
Contusions and hemorrhages in the left temporal lobe and infarctions of the posterior cerebral artery of the same hemisphere are common causes of sensory transcortical aphasia.
Transcortical motor aphasia also called “dynamic aphasia” and “prior isolation syndrome”. It occurs as a result of lesions in the triangular parts of the lower frontal lobe gyrus (Brodmann zone 45) or other parts of the dominant hemisphere for speech.
These cases are characterized by the preservation of the ability to name objects, understand language and repeat the words heard, as well as the presence of various alterations in speech production.
In transcortical motor aphasia, there is a reduction in the initiative to speak, accompanied by phenomena associated with repeating and imitating words pronounced by other people or by oneself, mainly perseverance, echolalia and palilalia.
Speech fluency is normal when the person repeats words and phrases or when calling out objects, although it is much less so during spontaneous speech.
Mixed aphasias are those that they have significant motor symptoms (That is to say those related to the production of language and writing) but also sensory (reception and understanding of speech and reading).
We speak of mixed transcortical aphasia when these signs appear without impairing the ability to repeat words and sentences appearing together. Otherwise, we would be referring to global aphasia, which is associated with very extensive damage to the left hemisphere of the brain.
In that case lesions appear in the frontal and parietal lobes of the left hemisphere, While the key regions for the language are not affected. This is why this type of aphasia is sometimes called “language isolation syndrome”.
As in transcortical motor aphasia, in mixed aphasia, fluidity is also normal on repetition but it is very altered in spontaneous emission. Echolales and other similar involuntary recurrences are also detected.