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neuroscience Neuroscience is the science, scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a Multidisciplinary approach, multidisciplinary science that combines physiology, an ...
and
psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...
, the term language center refers collectively to the areas of the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
which serve a particular function for
speech processing Speech processing is the study of speech signals and the processing methods of signals. The signals are usually processed in a digital representation, so speech processing can be regarded as a special case of digital signal processing, applied t ...
and production.
Language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of ...
is a core system, which gives humans the capacity to solve difficult problems and provides them with a unique type of
social interaction A social relation or also described as a social interaction or social experience is the fundamental unit of analysis within the social sciences, and describes any voluntary or involuntary interpersonal relationship between two or more individuals ...
. Language allows individuals to attribute
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
s (e.g. words or signs) to specific concepts and display them through sentences and
phrase In syntax and grammar, a phrase is a group of words or singular word acting as a grammatical unit. For instance, the English expression "the very happy squirrel" is a noun phrase which contains the adjective phrase "very happy". Phrases can consi ...
s that follow proper grammatical rules. Moreover,
speech Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...
is the mechanism in which language is orally expressed. Information is exchanged in a larger system including language-related regions. These regions are connected by
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribu ...
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 area Wernicke's area (; ), also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to B ...
s, and the
angular gyrus The angular gyrus is a region of the brain lying mainly in the posteroinferior region of the parietal lobe, occupying the posterior part of the inferior parietal lobule. It represents the Brodmann area 39. Its significance is in transferring ...
.


Broca's area

Broca's Area was first suggested to play a role in speech function by the French neurologist and anthropologist
Paul Broca Pierre Paul Broca (, also , , ; 28 June 1824 – 9 July 1880) was a French physician, anatomist and anthropologist. He is best known for his research on Broca's area, a region of the frontal lobe that is named after him. Broca's area is involve ...
in 1861. The basis for this discovery was the analysis of speech problems resulting from injuries to this region of the brain, located in the inferior frontal gyrus. Paul Broca had a patient called Leborgne who could only pronounce the word "tan" when speaking. Paul Broca, after working with another patient with similar impairment, 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 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, its particular 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 in the phonological processing (Bohsali, 2015). Moreover, 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, which are 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 Language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the sa ...
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 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 Carl (or Karl) Wernicke (; ; 15 May 1848 – 15 June 1905) was a German physician, anatomist, psychiatrist and neuropathologist. He is known for his influential research into the pathological effects of specific forms of encephalopathy and also ...
, who discovered it in 1874 in the course of his research into
aphasia Aphasia is an inability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in ...
s (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, the activation of 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. The communicative speech production entails a phase preceding phonological retrieval. The speech comprehension implicates representing sequences of phonemes onto word meaning.


Angular gyrus

The angular gyrus is an important element in processing concrete and abstract concepts. It also has a role in verbal working memory during retrieval for verbal information and in visual memory for when turning written language into spoken language. The left AG is activated in semantic processing requiring concept retrieval and conceptual integration. Moreover, the left AG is activated during problems of multiplication and addition requiring retrieval of arithmetic factors in verbal memory. Therefore, 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, linguistic, sensory, and limbic brain areas. The knowledge about the function of the insula in speech production comes from different studies with patients who had apraxia of speech. These studies have led researchers to know about 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, involved in misleading speech comprehension.


Speech and language disorders

Many different sources state that the study of the brain and therefore, language disorders, originated in the 19th century and linguistic analysis of those disorders began throughout the 20th century. Studying language impairments in the brain after injuries aids to comprehend how the brain works and how it changes after an injury. When this happens, the brain has an impairment that is referred to as "aphasia". Lesions to Broca's Area resulted primarily in disruptions to speech production; damage to Wernicke's Area, which is located in the lower part of the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved i ...
, lead mainly to disruptions in speech reception. There are numerous distinctive ways in which language can be affected. Phonemic paraphasia, an attribute of conduction aphasia and Wernicke aphasia, is not the speech comprehension impairment. Instead, it is the speech production damage, where the desire phonemes are selected erroneously or in an incorrect sequence. Therefore, although Wernicke's aphasia, a combination of phonological retrieval and semantic systems impairment, affects speech comprehension, it also involves speech production damage. Phonemic paraphasia and anomia (impaired word retrieval) are the results of phonological retrieval impairment. Another lesion that involves impairment in language production and processing is the "apraxia of speech", a difficulty synchronizing articulators essential for speech production. This lesion is located in the superior pre-central gyrus of the insula and is more likely to occur to patients with Broca's aphasia. Dominant ventral anterior (VA) nucleus, another type of lesion, is the result of word-finding and semantic paraphasia's difficulties engaging in language processing. Moreover, individuals with thalamic lesions experience difficulties linking semantic concepts with correct phonological representations in word production. Dyslexia is a language processing disorder. It involves learning difficulties such as reading, writing, word recognition, phonological recording, numeracy, and spelling. Although having access to appropriate intervention during childhood, these difficulties continue throughout the lifespan. Moreover, children are diagnosed with dyslexia when more than one factor affecting learning, such as reading, appears visible. Children diagnosed with dyslexia that have difficulties in concrete cognitive functioning is called an assumption of specificity, and it helps to diagnose dyslexia. Some characteristics that distinguish dyslexics are incompetent phonological processing abilities causing misread of unfamiliar words and affecting comprehension; inadequacy of working memory affecting speaking, reading, and writing; errors in oral reading; oral skills difficulties as expressing oneself; and writing skills problems like expressing and spelling errors. Dyslexics not only experience learning difficulties but also other secondary characteristics as having difficulties organizing, planning, social interactions, motor skills, visual perception, and short-term memory. These characteristics affect personal and academic life. Dysarthria is a motor speech disorder caused by damage in the central and/or peripheral nervous system and it is related to degenerative neurological diseases, such as Parkinson's disease, cerebrovascular accident (CVA) and traumatic brain injury (TBI). Dysarthria is caused by a mechanical difficulty in the vocal cords or neurological disease-producing abnormal articulation of phonemes, such as instead of "b" a "p". A type of dyspraxia based on distortions of words is called apraxic dysarthria This type is related to facial apraxia and motor aphasia if Broca's area is involved.


Current scientific consensus

Improvements in computer technology, in the late 20th century, has allowed a better understanding of the correlation between brain and language, and the disorder that this entails. This improvement has permitted a better visualization of the brain structure in high resolution three-dimensional images. It has also allowed to observe brain activity through the blood flow (Dronkers, Ivanova, & Baldo, 2017). New medical imaging techniques such as
PET A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
and
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area ...
have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. Functional magnetic resonance imaging (fMRI) is a technique used for locating, in the brain, particular functions to different activity related. This technique shows the location and magnitude of neural activity variations, influenced by external stimulation and fluctuation at rest. MRI is a technique that was developed in the 20th century to observe brain activity in healthy and abnormal brains. Diffusion-weighted magnetic resonance imaging or diffusion tensor imaging (DTI) is a technique use for track white matter bundles ''in vivo'' and gives information of the internal fibrous structure by the measure of water diffusion. This diffusion tensor is used for infer white matter connectivity. In the past, research was primarily based on observations of loss of ability resulting from damage to the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
. Indeed, medical imaging has represented a radical step forward for research on speech processing. Since then, a whole series of relatively large areas of the brain are involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the
putamen The putamen (; from Latin, meaning "nutshell") is a round structure located at the base of the forebrain (telencephalon). The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that compose the basal ...
and the
caudate nucleus The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's d ...
), as well as the pre-motor areas ( BA 6), have received increased attention. It is now generally assumed that the following structures of the cerebral cortex near the primary and secondary auditory cortices play a fundamental role in speech processing: ·       ''
Superior temporal gyrus The superior temporal gyrus (STG) is one of three (sometimes two) gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear. The superior temporal gyrus is bounded by: * the l ...
'' (STG):
morphosyntactic In linguistics, morphology () is the study of words, how they are formed, and their relationship to other words in the same language. It analyzes the structure of words and parts of words such as stems, root words, prefixes, and suffixes. Morph ...
processing (anterior section), integration of
syntactic In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure (constituency) ...
and
semantic Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comput ...
information (posterior section) ·       ''
Inferior frontal gyrus The inferior frontal gyrus (IFG), (gyrus frontalis inferior), is the lowest positioned gyrus of the frontal gyri, of the frontal lobe, and is part of the prefrontal cortex. Its superior border is the inferior frontal sulcus (which divides it f ...
'' (IFG,
Brodmann area A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. History Brodmann areas were originally defined and numbered by th ...
(BA) 45/ 47): syntactic processing,
working memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...
·       ''
Inferior frontal gyrus The inferior frontal gyrus (IFG), (gyrus frontalis inferior), is the lowest positioned gyrus of the frontal gyri, of the frontal lobe, and is part of the prefrontal cortex. Its superior border is the inferior frontal sulcus (which divides it f ...
'' (IFG, BA 44): syntactic processing, working memory ·       ''
Middle temporal gyrus Middle temporal gyrus is a gyrus in the brain on the temporal lobe. It is located between the superior temporal gyrus and inferior temporal gyrus. It corresponds largely to Brodmann area 21. The middle temporal gyrus is bounded by: * the superi ...
'' (MTG): lexical semantic processing ·       Angular gyrus (AG): semantic processes (posterior temporal cortex) The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in the area of syntactic processing. It is now accepted that the right hemisphere plays an important role in the processing of suprasegmental acoustic features like prosody; which is "the rhythmic and melodic variations in speech". There are two types of prosodic information: emotional prosody (right hemisphere), which is the emotional that the speaker gives to the speech, and linguistic prosody (left hemisphere), the syntactic and thematic structure of the speech. Most areas of speech processing develop in the second year of life in the dominant half (
hemisphere Hemisphere refers to: * A half of a sphere As half of the Earth * A hemisphere of Earth ** Northern Hemisphere ** Southern Hemisphere ** Eastern Hemisphere ** Western Hemisphere ** Land and water hemispheres * A half of the (geocentric) celes ...
) of the brain, which often (though not necessarily) corresponds to the opposite of the dominant hand. 98% of right-handed people are left-hemisphere dominant, and the majority of left-handed people are as well. Computerized tomographic (CT) scans is another technique of the 1970s, which produce low spatial resolution but provides the location of the injury ''in vivo''. Moreover, Voxel-based Lesion Symptom Mapping (VLSM) and Voxel-Based Morphometry (VBM) techniques contributed to the understanding that specific brain regions have different roles when supporting speech processing. VLSM has been used to observe complex language functions sustained by different regions. Furthermore, VBM is a helpful technique to analysis language impairments related to neurodegenerative disease.


Older models

The differentiation of speech production into only two large sections of the brain (i.e. Broca's and Wernicke's areas), that was accepted long before the advent of medical imaging techniques, is now considered outdated. 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 the analysis of speech problems resulting from injuries to this region of the brain, located in the inferior frontal gyrus. Lesions to Broca's Area resulted primarily in disruptions to speech production. Damage to Wernicke's Area, which is located in the lower part of the
temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved i ...
, lead mainly to disruptions in speech reception. This area was named for German doctor
Carl Wernicke Carl (or Karl) Wernicke (; ; 15 May 1848 – 15 June 1905) was a German physician, anatomist, psychiatrist and neuropathologist. He is known for his influential research into the pathological effects of specific forms of encephalopathy and also ...
, who discovered it in 1874 in the course of his research into
aphasia Aphasia is an inability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine but aphasia due to stroke is estimated to be 0.1–0.4% in ...
s (loss of ability to speak). Broca's Area is today still considered an important language center, playing a central role in processing syntax, grammar, and sentence structure. In summary, these early research efforts demonstrated that semantic and structural speech production takes place in different areas of the brain.


See also

*
Language module The language module or language faculty is a hypothetical structure in the human brain which is thought to contain innate capacities for language, originally posited by Noam Chomsky. There is ongoing research into brain modularity in the fields o ...


References


Further reading

* Donald Loritz: ''How the Brain evolved Language'', Oxford University Press 1999, (hardcover), (paperback) * Friederici, A.D.:
Towards a neural basis of auditory sentence processing
'. Trends in Cognitive Sciences, 6:78, 2002. * Kaan, E. and Swaab, T.Y.:
The brain circuitry of syntactic comprehension
'' Trends in Cognitive Sciences, 6:350, 2002. * Dronkers, N.F., Pinker, S. & Damasio, A.: ''Language and the Aphasias.'' In: Kandel, E.R., Schwartz, J.H. & Jessel, T.M. (eds.) Principles of Neuroscience, Fourth Edition, New York: McGraw-Hill, 2000, 1169–1187 *Ardila, A., Bernal, B. and Rosselli, M.
How localized are language brain areas? A review of Brodmann areas involvement in oral language
" Archives of Clinical Neuropsychology, 31(1), 112–122, 2016. {{Authority control Neurolinguistics Neuropsychology Psycholinguistics