Stroke - What is Wernicke’s Aphasia?
In this fourth article, in the series on aphasia, let’s examine Wernicke’s aphasia, also known as sensory aphasia or fluent aphasia. For readers of this column, who may not be familiar with my previous articles, I will define aphasia again.
Aphasia, also called dysphasia, is a defect in the expression and comprehension of language, caused by damage from a head injury, tumor, stroke, or infection, to the temporal and the frontal lobes of the brain.
The Wernicke region of the brain contains motor neurons involved in the comprehension of speech. This area was first described in 1874, by German neurologist, Carl Wernicke and is located in the posterior third of the upper temporal convolution of the left hemisphere of the brain, close to the auditory cortex. This area appears to be uniquely important for the comprehension of speech sounds and is considered to be the receptive hub of language and language comprehension. Thus, damage to the temporal lobe may result in several language disorders, such as Wernicke’s aphasia.
Patients with Wernicke’s aphasia, know what they want to say, but have difficulty saying or writing what they mean. As a result, such patients suffer from a severe impairment of understanding spoken or written words, including their own.
It must be borne in mind, that patients with all subtypes of aphasia aren’t learning how to use language all over again, they are working hard to gradually unlock what is already stored in their memory.
This type of aphasia is associated with fluent language output that is severely disorganized. In such cases, fluency refers to people with receptive aphasia that can speak with the conventional use of grammar, syntax, rate, intonation and stress, although their language content may not always make sense. For example, patients may use incorrect words, insert non-existent words into speech or string conventional words together into a random sequence. The speech of people with this condition as well as reading skills and written words are fluent, but “meaningless”.
A patient afflicted with receptive aphasia, can hear the sound of voices and can read printed words in books, newspapers and magazines, but may not understand the meaning of the message. Pure word blindness, denotes patients whose auditory comprehension is intact, but reading is impaired. These patients can understand speech better than words on a printed page.
Although reading is severely compromised in many patients, some of them may read text better than they understand speech. This is described as pure word deafness.
There was an instance in which a 65 year old man was referred to the Neurology Unit of Johannesburg General Hospital, for assessment of a hearing problem that occurred suddenly. He could not understand speech, although he could hear other sounds clearly. In a puzzling twist, he retained the ability to sing, or to recite a memorized poem of prose piece. This is a characteristic of pure word deafness.