In neuroscience and psychology, the term language center refers collectively to the areas of the brain which serve a particular function for speech processing and production. Language is a core system that gives humans the capacity to solve difficult problems and provides them with a unique type of social interaction. Language allows individuals to attribute symbols (e.g. words or signs) to specific concepts, and utilize them through sentences and phrases that follow proper grammatical rules. Finally, speech is the mechanism by which language is orally expressed. Information is exchanged in a larger system, including language-related regions. These regions are connected by white matter fiber tracts that make possible the transmission of information between regions. The white matter fiber bunches were recognized to be important for language production after suggesting that it is possible to make a connection between multiple language centers. The three classical language areas that are involved in language production and processing are Broca's and Wernicke's areas, and the angular gyrus.
Broca's area
Broca's Area was first suggested to play a role in speech function by the French neurologist and anthropologist Paul Broca in 1861. The basis for this discovery was analyzing speech problems resulting from injuries to this brain region, located in the inferior frontal gyrus. Paul Broca had a patient called Leborgne who could only pronounce the word "tan" when speaking. After working with another patient with a similar impairment, Paul Broca concluded that damage in the inferior frontal gyrus affected articulate language. Broca's area is well known for being the syntactic processing "center". It has been known of since Paul Broca associated speech production with an area in the posterior inferior frontal gyrus, which he called "Broca's area". Although this area is in charge of speech production, the specific details of its role in the language system is unknown. However, it is involved in phonological, semantic, and syntactic processing, and working memory. The anterior region of Broca's area is involved in semantic processing, while the posterior region involves phonological processing (Bohsali, 2015). The whole of Broca's area has been shown to have a higher activation while doing reading tasks than other types of tasks. In a simple explanation of speech production, this area approaches phonological word representation chronologically divided into segments of syllables which then is sent to different motor areas where they are converted into a phonetic code. The study of how this area produces speech has been made with paradigms using both single and complex words. Broca's area is correlated with phonological segmentation, unification, and syntactic processing, all connected to linguistic information. This area, although it synchronizes the transformation of information within cortical systems involved in spoken word production, does not contribute to the production of single words. The inferior frontal lobe is the one in charge of word production. Furthermore, Broca's area is structurally related to the thalamus, and both are engaged in language processing. The connectivity between both areas is two thalamic nuclei, the pulvinar, and the ventral nucleus, which are involved in language processing and linguistic functions similar to BA 44 and 45 in Broca's area. Pulvinar is connected to many frontal regions of the frontal cortex and the ventral nucleus is involved in speech production. The frontal speech regions of the brain have been shown to participate in speech sound perception. Broca's Area is today still considered an important language center, playing a central role in processing syntax, grammar, and sentence structure.
Wernicke's area Wernicke's area was named for German doctor Carl Wernicke, who discovered it in 1874 in the course of his research into aphasias (loss of ability to speak). This area of the brain is involved in language comprehension. Therefore, Wernicke's area is for understanding oral language. Besides Wernicke's area, the left posterior superior temporal gyrus (pSTG), middle temporal gyrus (MTG), inferior temporal gyrus (ITG), supramarginal gyrus (SMG), and angular gyrus (AG) participate in language comprehension. Therefore, language comprehension is not located in a specific area. Contrarily, it involves large regions of the inferior parietal lobe and left temporal. While the finale of speech production is a sequence of muscle movements, activating knowledge about the sequence of phonemes (consonants and vowel speech sounds) that creates a word is a phonological retrieval. Wernicke's area contributes to phonological retrieval. All speech production tasks (e.g. word retrieval, repetition, and reading aloud) require phonological retrieval. The phonological retrieval system involved in speech repetition is the auditory phoneme perception system, and the visual letter perception system is the one that serves for reading aloud. Communicative speech production entails a phase preceding phonological retrieval. Speech comprehension involves mapping sequences of phonemes onto word meaning.
Angular gyrus (Inferior parietal lobule)
The angular gyrus is important in processing concrete and abstract concepts. It also has a role in verbal working memory during retrieval of verbal information and in visual memory when turning written language into spoken language. The left AG is activated in semantic processing that requires concept retrieval and conceptual integration. Also, the left AG is activated during problems of multiplication and addition requiring return of arithmetic factors in verbal memory. Thus, it is involved in verbal coding of numbers.
Insular cortex
The insula is implicated in speech and language, taking part in functional and structural connections with motor neurons, linguistic, sensory, and limbic brain areas. The knowledge about the function of the insula in speech production comes from different studies with patients having speech apraxia. These studies have led researchers to learn of the involvement of different parts of the insula. These parts are the left anterior insula, which is related to speech production, and the bilateral anterior insula, which is involved in misleading speech comprehension.
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