Transcortical aphasia (sensory, motor and mixed)

One of the most characteristic disorders of brain damage is aphasia, which is defined as a impaired 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 features of the three types of transcortical aphasia: sensory, motor and mixed. By way of introduction we will briefly explain the general features of aphasias, especially the transcortical ones.

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What is transcortical aphasia?

Aphasias are language disorders that appear as a consequence of lesions in regions of the left hemisphere of the brain related to speechas well as reading and writing. However, in some people the language is more distributed between the two hemispheres, as is the case with left-handers, and the left is not dominant.

The most frequent causes of aphasia are ischemic cerebrovascular accidents, head injuries and neurodegenerative diseases, including dementias.

In the context of aphasia the term “transcortical” refers to the appearance of damage in various lobes of the brain that isolate some nerve 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 greatly depending on the type to which we refer (sensory, motor or mixed). However, the three classes 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 feature distinguishes transcortical aphasias from other variants of this disorder, particularly Broca's or motor aphasia, Wernicke's or sensory, conduction and global or total. Beyond this, the usual signs of transcortical aphasias are similar to those of the rest.

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Types of transcortical aphasia

Three types of transcortical aphasia have been distinguished based on the relative predominance of symptoms and signs related to comprehension and language production.

Thus, we find transcortical sensory, motor and mixed aphasia, in which both kinds of alteration are present to a severe degree.

1. sensory

sensory transcortical aphasia characterized by poor language comprehension, 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.

Both in Wernicke's aphasia and in 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 production meaningless verbal.

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 Silvio fissure or lateral groove of the brain, one of its most important folds.

Bruises and hemorrhages in the left temporal lobe and infarcts in the posterior cerebral artery of the same hemisphere are common causes of transcortical sensory aphasia.

2. Motorboat

transcortical motor aphasia It is also known as "dynamic aphasia" and "prior isolation syndrome".. It occurs as a consequence 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 conservation of the capacities to name objects, understand language and repeat words that are heard, as well as by 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 names objects, although it is much less so during spontaneous speech.

3. Mixed

Mixed aphasias are those that have significant motor symptoms (that is, those related to the production of language and writing) but also sensory (reception and comprehension of speech and reading).

We speak of mixed transcortical aphasia when these signs appear without the 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 in the left hemisphere of the brain.

In this case lesions appear in the frontal and parietal lobes of the left hemisphere, although the regions fundamental to 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 it is greatly altered in spontaneous emission. Echolalia and other similar involuntary repetitions are also detected.