One of the most characteristic disorders of brain damage is aphasia, which is defined as an alteration in the ability to understand and/or produce oral and written language . There is a special type of aphasia that is characterised by the maintenance of the ability to repeat words that have been heard; this is called transcortical aphasia.

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 features of aphasia, especially transcortical aphasia.

What is transcortical aphasia?

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 reading and writing. However, in some people the language is more distributed between the two hemispheres, as is the case with left-handed people, and the left one is not the dominant one.

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 various lobes of the brain that isolates 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 aphasia vary greatly depending on the type of aphasia (sensory, motor or mixed). However, a common feature of all three types of transcortical aphasia is the maintenance of the ability to repeat words or phrases that have been uttered by others.

This feature distinguishes transcortical aphasia from other variants of this disorder, particularly Broca’s aphasia or motor, Wernicke’s aphasia or sensory, conductive and global or total aphasia. Beyond this, the usual signs of transcortical aphasia are similar to those of the rest .

Types of transcortical aphasia

Three types of transcortical aphasia have been distinguished according to the relative predominance of symptoms and signs related to language understanding and production.

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

1. Sensory

Transcortical sensory aphasia is characterised by poor understanding of language , whether manifested in speech or reading, as well as by the maintenance of verbal fluency. These signs are very similar to those of Wernicke’s aphasia, although in this case the repetition is altered.

Both in Wernicke’s aphasia and in transcortical sensory articulation of phonemes are correct, although the speech tends to be full of meaningless terms (neologisms) as well as unnecessary syllables and words (paraphrases) that detract from the verbal production.

This type of aphasia is associated with lesions at the inferior 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 Silvio’s cleft or lateral brain furrow, one of its most important folds.

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

2. Motorcycle

Transcortical motor aphasia is also known as “dynamic aphasia” and “anterior isolation syndrome” . It occurs as a result of lesions in the pars triangularis of the lower frontal lobe gyrus (Brodmann’s area 45) or other parts of the dominant hemisphere for language.

These cases are characterized by the preservation of the abilities to name objects, understand language and repeat words that are heard, as well as by the presence of various alterations in the production of speech.

In transcortical motor aphasia there is a reduction in the initiative to speak, accompanied by phenomena associated with repetition and imitation of words pronounced by other people or by oneself, mainly perseveration, echolalia and palilalia.

Fluency of speech is normal when the person repeats words and phrases or calls out objects, although it is much less so during spontaneous speech.

3. Mixed

Mixed aphasias are those which present significant symptoms of a motor nature (i.e. those related to the production of language and writing) but also of a sensory nature (reception and comprehension of speech and reading).

We speak of mixed transcortical aphasia when these signs occur without a joint 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 that are fundamental 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 the fluidity is also normal when repeating but it is very altered in spontaneous emission. Echolalia and other similar involuntary repetitions are also detected.