Carl Wernicke: Image source: Wikimedia
This journey (Journeys to the brain-13) travels through this speech problem that stroke can cause: Wernicke aphasia. It is also called “fluent aphasia”.
What is Wernicke aphasia?
In 1874 – after Paul Broca’s discovery of the Broca area and Broca aphasia – Carl Wernicke described a different type of aphasia. This type allows the affected to talk at their usual speed, but words and sentences do not convey any meaning. Anyone can notice the problem. And, they repeat the same word over and over again.
According to Argyle E. Hillis, they seem unaware of their errors. The listener might think that the affected is are talking in another language that the listener cannot understand. Not only talking but writing and reading follow a similar pattern. Hence, this type of aphasia is called fluent aphasia (Broca aphasia is called non-fluent aphasia). Since Carl Wernicke described this, it is also called Wernicke aphasia.
You can find out how an individual with Wernicke aphasia converses with others by watching this video clip.
The Wernicke aphasia occurs as a result of damage to the Wernicke area. Where is it in the brain?
The Wernicke area lies in the temporal lobe. You can find the temporal lobe in this walk over the brain surface in the journeys to the brain – 2. The Wernicke area lies at a place close to the area (auditory) that contains cells specialized in processing hearing information (Figure 1). Whenever we hear something, the hearing area receives information from the ear and then sends those to the Wernicke area. Similarly, whenever we see or read something, the visual area sends that information to the Wernicke area. Neurons in this area retrieve suitable nouns appropriate to the context from the storeroom, set the language structure, and shoot that to Broca’s area. Broca’s area processes it to produce speech.
How do Wernicke’s neurons connect with Broca’s neurons?
As shown in Figure 2, Wernicke neurons connect with Broca’s neurons through a super-highway, called “arcuate Fasciculus”. This bundle of neurons transmit messages between the two speech processing areas.
How do neurons’ in the Wernicke area die?
Wernicke’s neurons die due to disruption of the blood supply to the temporal lobe where the Wernicke area resides. Most commonly, a blood clot that blocks a branch (the inferior branch) of the left middle cerebral artery is the culprit.