One of the most characteristic disorders of brain damage is aphasia, which is defined as a alteration in the ability to understand and/or produce oral and written language. There is a special type of aphasia that is characterized by the maintenance of the ability to repeat words that have been heard; These are transcortical aphasias.
In this article we will describe the main characteristics of the three types of transcortical aphasia: sensory, motor and mixed. As an introduction we will briefly explain the general features of aphasias, especially transcortical ones.
Aphasias are language disorders that appear as a result of lesions in regions of the left hemisphere of the brain related to speech, as well as with reading and writing. However, in some people language is more distributed between the two hemispheres, as is the case with left-handed people, and the left one is not dominant.
The most common causes of aphasia are ischemic strokes, head injuries, and neurodegenerative diseases, including dementia.
In the context of aphasia The term “transcortical” refers to the appearance of damage in several lobes of the brain that isolate some pathways and neural structures related to language. The function of these regions is preserved, which explains the symptomatic peculiarities of these aphasias.
The signs of transcortical aphasia vary greatly depending on the type we are referring to (sensory, motor or mixed). However, the three types of transcortical aphasia present as a common feature the maintenance of the ability to repeat words or phrases that have been pronounced by other people.
This characteristic distinguishes transcortical aphasias from other variants of this disorder, particularly Broca’s or motor aphasia, Wernicke’s or sensory aphasia, conduction aphasia, and global or total aphasia. Beyond this, The usual signs of transcortical aphasias are similar to those of the rest.
Types of transcortical aphasia
Three types of transcortical aphasia have been distinguished based on the relative predominance of symptoms and signs related to language comprehension and production.
Thus, we find transcortical sensory, motor and mixed aphasia, in which both types of alteration are present to a severe degree.
1. Sensory
Sensory transcortical aphasia It is characterized by poor understanding of language, whether it manifests itself in speaking or reading, as well as by maintaining verbal fluency. These signs are very similar to those of Wernicke’s aphasia, although in this the repetition is altered.
In both Wernicke’s aphasia and transcortical sensory aphasia, the articulation of phonemes is correct, although the speech tends to be full of meaningless terms (neologisms) as well as unnecessary syllables and words (paraphasias) that make the verbal production meaningless.
This type of aphasia It is associated with lesions in the lower part of the junction between the temporal, parietal and occipital lobes, which correspond to areas 37 and 39 of the classification made by Brodmann. In this part of the brain we find the Sylvian fissure or lateral sulcus of the brain, one of its most important folds.
Contusions and hemorrhages in the left temporal lobe and infarcts in the posterior cerebral artery of the same hemisphere are common causes of sensory transcortical aphasia.
Transcortical motor aphasia It is also known as “dynamic aphasia” and “anterior isolation syndrome.”. It occurs as a result of lesions in the pars triangularis of the inferior gyrus of the frontal lobe (Brodmann area 45) or other parts of the language-dominant hemisphere.
These cases are characterized by the preservation of the abilities to name objects, understand language and repeat words that are 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 the repetition and imitation of words pronounced by other people or by oneself, mainly perseveration, echolalia and palilalia.
Speech fluency is normal when the person repeats words and phrases or when naming objects, although it is much less so during spontaneous speech.
3. Mixed
Mixed aphasias are those that present significant motor symptoms (that is, 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 occur without a joint appearance of an alteration in the ability to repeat words and phrases. Otherwise we would be referring to global aphasia, which is associated with very extensive lesions of the left hemisphere of the brain.
In this case lesions appear in the frontal and parietal lobes of the left hemisphere, although the regions essential for language are not affected. This is why this type of aphasia is sometimes referred to as “language isolation syndrome.”
As in transcortical motor aphasia, in mixed aphasia fluency is also normal when repeating but is greatly altered in spontaneous emission. Echolalia and other similar involuntary repetitions are also detected.
