Transcortical motor aphasia

Transcortical motor aphasia (TMoA), also known as commissural dysphasia and white matter dysphasia, results from damage, typically due to cerebrovascular accident (CVA), in the anterior superior frontal lobe of the language-dominant hemisphere. The left hemisphere usually performs language functions, although left-handed individuals have been shown to perform language functions with both their right and left hemispheres. Damage in the watershed region does not directly damage the areas of the brain involved in language production or comprehension; instead, the damage isolates these areas from the rest of the brain. Due to damage in areas of the frontal lobe, executive functions related to language use are often affected in individuals with TMoA. Relevant executive functions include activating language responses and controlling syntax (grammar) and narrative discourse, which can lead to difficulties forming complex sentences, choosing which words to use appropriately, and initiating speech in conversation. The extent of brain damage will impact how much language functioning is impaired (i.e. damage deep to the frontal lobe and/or damage across multiple regions will greatly impair language). Right hemiparesis, which is right-sided paralysis, may occur along with TMoA if the lesion in the anterior frontal lobe is large enough and extends into the posterior frontal lobe. There are also other forms of aphasias that are a result of TMoA. Adynamic aphasia is one example; it is a form of TMoA characterized by sparse speech. Adynamic aphasia has normal spontaneous speech due to the fact that when new concepts are introduced by external stimuli, spontaneous speech improves. This is a result of executive functioning in the frontal lobe.

TMoA is a type of non-fluent aphasia with a lower occurrence than Broca’s aphasia. TMoA often resembles Broca’s but with preserved repetition. A person with TMoA may be echolalic and can repeat long complex phrases effortlessly. People with TMoA generally have good auditory comprehension since the arcuate fasciculus and Wernicke's area are not impaired. However, they have a reduced speech output due to damage in the left anterior superior frontal lobe. A person with TMoA has difficulty producing spontaneous speech and their utterances are usually one to two words long. When they do speak, their speech is well articulated although sparse. Initiation is also a problem due to damage in the prefrontal cortex. For instance, someone with TMoA might not be able to answer open-ended questions but would be able to answer yes/no questions.

...
Wikipedia