I’m going to talk about language in my next few posts, so here’s an overview of the language areas in our brain. As you will see, there’s a lot that goes on in a very short space of time for us to be able to understand speech and reply appropriately, but I’ll try and make it as simple as possible.
Here is a diagram of the brain showing the main areas involved in language processing. As you can see from the diagram, it is the left hemisphere which is specialised for language (the frontal lobe is on the left):
The auditory cortex is the part of the brain that processes speech, and enables us to make sense of it. The motor area then controls the vocal tract, throat, tongue and mouth so we can talk. Broca’s area, shown in purple on the diagram, is the inferior frontal gyrus, which is important for language production. Broca (1861) studied a patient who was unable to produce speech other than the word ‘tan’ and swear words, but could understand questions. This patient had a huge lesion in his inferior frontal cortex, so Broca concluded that this area is important for speech. He studied several patients with lesions in this area, and found that only those who had lesions in the left hemisphere had impaired speech, which shows that the left hemisphere is important for language. Patients with Broca’s Aphasia are able to produce single words but not full sentences.
Wernicke’s area is the posterior part of the superior temporal gyrus, and is important for speech understanding. Wernicke (1874) was the first to describe patients who had lost the ability to comprehend speech despite normal hearing, and could not produce meaningful speech despite normal articulation and grammar. Patients with Wernicke’s Aphasia have fluent speech but it is lacking any content or meaning.
This next diagram shows how Broca’s and Wernicke’s areas are thought to interact to produce speech, based on the Wernicke-Lichtheim Model:
The arcute fasiculus is the white matter that connects the two areas. If it is cut, then Conduction Aphasia occurs – this is when speech sounds and movements are unaffected, as well as normal comprehension, but repetition of speech is impaired.
Check back soon for my next post on how infants develop language abilities!