Broca's and Wernicke's areas
https:// en.wikipedia.org/wiki/Wernicke's_area

Wernicke's area

Wernicke's area is commonly located in the dominant hemisphere above the Sylvian fissure, in the posterior part of the superior temporal gyrus. It is responsible for pairing sounds and meanings. This comprises all sounds, whether linguistic or non-linguistic.

In speech perception, the area gets input from the auditory cortex and pairs the phonological form received with a meaning. It is, thus, involved in auditory word recognition. If it does not work properly ‐ notably in sensory aphasia –, the person does not understand speech. Because of these symptoms, Wernicke's area is often simplistically made responsible for the reception and comprehension, as opposed to production, of speech.

In speech production, Wernicke's area accesses lexical items for the mental units forming a thought, pairs a meaning with a phonological form and sends the signals thus selected to the motor cortex. If it does not work properly, it does not find the appropriate words and select the corresponding phonological forms, and instead sends everyday words or senseless strings to the motor cortex. Since semiotic matching is bidirectional, the feedback on this matching then does not work, either. As a result, persons affected by this disorder are not aware of it.

On balance, Wernicke's area is responsible for semiosis, for matching signs with their meaning. Wernicke's area has a homologous counterpart in the non-dominant hemisphere. This, too, is concerned with the processing of incoming sound, although not as a semiotic process of assigning it a meaning, but as an emotional reaction. It primarily processes music, but secondarily linguistic sound, too.

Broca's area

Broca's area is commonly located in the inferior frontal region of the dominant hemisphere. It is crucial in the serialization of complex structure.

In speech production, the area controls those motor aspects which concern temporal sequencing of units. It is not involved in the conception of a coherent thought or in word retrieval, but needed for the formation of phonological structures and grammatical constructions. The phonological configurations formed are sent to the motor cortex (in the frontal lobe) that will send motor signals to the speech apparatus. If Broca's area does not work properly ‐ notably in expressive aphasia –, errors at the phonetic level concern the sequencing of articulatory and phonatory gestures. At the level of grammar, phonological forms corresponding to individual words are then pronounced, without any grammatical structure. Because of these symptoms, Broca's area is often simplistically made responsible for the production, as opposed to reception, of speech.

Quite in general in perception, Broca's area is active if the person observes another person engaged in purposeful motion. In other words, the person perceives that another person is moving in a conventional way and infers what goals the other person is pursuing, thus understanding his intentions. The posterior part of Broca's area reacts to such percepts by a mirror-neuron subsystem. This function of Broca's area may be the basis of its specifically semiotic capacity: gestures are a kind of controlled movement which reveal an intention that the moving person is entertaining. Consequently, Broca's area is active in decoding sign language.

In speech comprehension, Broca's area is active in the analysis of received speech. Its posterior part executes phonological and structural analysis, while its anterior part executes semantic analysis. Both of these subareas activate short-term memory, but the anterior part also connects up with long-term memory.

Most neurological studies of Broca's area mention its role in the syntax of linguistic constructions and say nothing about morphology. This is presumably due to a bias in the researchers and to the peculiar nature of the language that most of the subjects spoke, viz. English. It seems probable that if there is an organ that manages (aspects of) the syntax of human language, it is responsible not for syntax in isolation, but instead for grammar.

On balance, Broca's area, in interaction with the basal ganglia, is responsible for the sequencing of operations. If these are linguistic operations, they produce phonological and grammatical constructions. These are mostly processed subconsciously and automatically.

Conclusion

The language faculty does not reside exclusively in these two areas. Among other parts of the brain, the basal ganglia control the sequencing not only of movements, but of operations in general (Lieberman 2002). Although different areas in the brain are specialized for different functions, there is no single area in the brain which would contain a language module. Instead, speech production and perception result from the interaction of different parts of the brain. The language faculty emerges from the combination of diverse cognitive and communicative capacities.