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.[1]Language is a core system that gives humans the capacity to solve difficult problems and provides them with a unique type of social interaction.[2] 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.[2] Finally, speech is the mechanism by which language is orally expressed.[2]
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.[3] 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.[3] 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 was first suggested to play a role in speech function by the French neurologist and anthropologistPaul 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.[2] 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.[2]
Broca's area is well known for being the syntactic processing "center".[2] 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".[4] Although this area is in charge of speech production, the specific details of its role in the language system is unknown.[4] However, it is involved in phonological, semantic, and syntactic processing, and working memory.[5] 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.[6]
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.[4] The study of how this area produces speech has been made with paradigms using both single and complex words.[4]
Broca's area is correlated with phonological segmentation, unification, and syntactic processing, all connected to linguistic information.[4] 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.[4] The inferior frontal lobe is the one in charge of word production.[4]
Furthermore, Broca's area is structurally related to the thalamus, and both are engaged in language processing.[5] 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.[5] Pulvinar is connected to many frontal regions of the frontal cortex and the ventral nucleus is involved in speech production.[5] The frontal speech regions of the brain have been shown to participate in speech sound perception.[5]
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 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.[7] Therefore, Wernicke's area is for understanding oral language.[8] 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.[7]
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.[7] 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.[7] Communicative speech production entails a phase preceding phonological retrieval. Speech comprehension involves mapping sequences of phonemes onto word meaning.[7]
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.[9] 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.[9]
The insula is implicated in speech and language, taking part in functional and structural connections with motor neurons, linguistic, sensory, and limbic brain areas.[10] 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.[10]
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 in the 20th century.[2] Studying language impairments in the brain after injuries aids in comprehending how the brain works and changes after an injury. When this happens, the brain's impairment is referred to as "aphasia".[2]Lesions to Broca's Area results primarily in disruptions to speech production; damage to Wernicke's Area, which is located in the lower part of the temporal lobe, leads 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, does not involve speech comprehension impairment. Instead, it requires speech production damage, where the desired phonemes are selected erroneously or in an incorrect sequence.[7] Therefore, although Wernicke's aphasia, a combination of phonological retrieval and semantic systems impairment, affects speech comprehension, it also involves speech production damage.[7] Phonemic paraphasia and anomia (impaired word retrieval) are the results of phonological retrieval impairment.[7]
Another lesion that involves impairment in language production and processing is "apraxia of speech", a difficulty synchronizing articulators essential for speech production.[2] This type of lesion is located in the superior pre-central gyrus of the insula, and is more likely to occur in patients with Broca's aphasia.[2] Dominant ventral anterior (VA) nucleus, another type of lesion, is the result of word-finding and semantic paraphasia's difficulties engaging in language processing.[needs copy edit][clarification needed][5] Also, individuals with thalamic lesions experience difficulties linking semantic concepts with correct phonological representations in word production.[5]
Dyslexia is a language-processing disorder. It involves learning difficulties in reading, writing, word recognition, phonological recording, numeracy, and spelling. Even with access to appropriate intervention during childhood, these difficulties continue throughout the lifespan.[11] Children are diagnosed with dyslexia when more than one factor affecting learning (e.g. reading or writing) appears. When children diagnosed with dyslexia have difficulties in concrete cognitive functioning, this is called an assumption of specificity, and it aids in the diagnosis of dyslexia.[11]
Some characteristics that distinguish dyslexics include errors in phonological processing, causing misreading of unfamiliar words, affecting comprehension; inadequacy of working memory, affecting speaking, reading, and writing; errors in oral reading; oral skill difficulties such as expressing oneself; and writing skill problems in areas such as spelling and general expression.[12] Dyslexics not only experience learning difficulties, but also other secondary characteristics, such as having difficulties in organizing, planning, social interaction, motor skills, visual perception, and short-term memory. These characteristics affect personal and academic life.[11]
Dysarthria is a motor speech disorder caused by damage to 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).[13]Dysarthria can be caused by a mechanical difficulty in the vocal cords, or neurological disease, and produces abnormal articulation of phonemes, such as using "b" in place of "p".[13] Apraxic dysarthria is a type of dyspraxia that involves distortions of words.[13] This type is related to facial apraxia and motor aphasia if Broca's area is involved.[clarification needed][13]
Current scientific consensus
Improvements in computer technology in the late 20th century has allowed a better understanding of the correlation between brain and language, in the disorders that this entails.[2] This improvement has permitted better visualization of the brain structure in high-resolution three-dimensional images. It has also allowed observation of brain activity through blood flow (Dronkers, Ivanova, & Baldo, 2017).[2]
New medical imaging techniques such as PET and fMRI have allowed researchers to generate pictures showing which areas of a living brain are active at a given time. Functional magnetic resonance imaging (fMRI) localizes specific brain functions to particular brain regions by observing blood flow in different areas.[3] This technique shows the location and magnitude of neural activity variations, influenced by external stimulation and fluctuation at rest.[3] MRI is a technique that was developed in the 20th century to observe brain activity in healthy and abnormal brains.[2] Diffusion-weighted magnetic resonance imaging, or diffusion tensor imaging (DTI), is a technique used for tracking white matter bundles in vivo, and gives information on the internal fibrous structure via measuring water diffusion. This diffusion tensor is used for inferring white matter connectivity.[3]
In the past, research was primarily based on observations of loss of ability resulting from damage to the cerebral cortex. In the modern era, medical imaging has represented a radical step forward for research on speech processing. It is now known that a whole series of relatively large brain areas are involved in speech processing. In more recent research, subcortical regions (those lying below the cerebral cortex such as the putamen and the caudate nucleus), 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:
The left hemisphere is usually dominant in right-handed people, although bilateral activations are not uncommon in 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".[3] There are two types of prosodic information: emotional prosody (right hemisphere), which is the emotional content of the speech, and linguistic prosody (left hemisphere), the syntactic and thematic structure of the speech.[3]
Most areas of speech processing develop in the second year of life in the dominant half (hemisphere) 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 are a technique dating to the 1970s, and produce low spatial resolution, but are capable of providing the location of injuries in vivo.[2] Also, Voxel-based Lesion Symptom Mapping (VLSM) and Voxel-Based Morphometry (VBM) techniques have contributed to the understanding that specific brain regions have different roles when supporting speech processing.[2] VLSM has been used to observe complex language functions supported by multiple brain regions. VBM is a helpful technique for analyzing language impairments related to neurodegenerative disease.[2]
Older models
The differentiation of speech production into only two large sections of the brain (i.e. Broca's and Wernicke's areas), which was accepted long before 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 brain region, located in the inferior frontal gyrus. Lesions to Broca's Area result primarily in disruptions to speech production.
Damage to Wernicke's Area, located in the lower part of the temporal lobe, mainly leads to speech reception disruptions. This 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).
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 occurs in different brain areas.
In aphasia, a person may be unable to comprehend or unable to 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 the Global North. Aphasia can also be the result of brain tumors, epilepsy, autoimmune neurological diseases, brain infections, or neurodegenerative diseases.
Wernicke's aphasia, also known as receptive aphasia, sensory aphasia, fluent aphasia, or posterior aphasia, is a type of aphasia in which individuals have difficulty understanding written and spoken language. Patients with Wernicke's aphasia demonstrate fluent speech, which is characterized by typical speech rate, intact syntactic abilities and effortless speech output. Writing often reflects speech in that it tends to lack content or meaning. In most cases, motor deficits do not occur in individuals with Wernicke's aphasia. Therefore, they may produce a large amount of speech without much meaning. Individuals with Wernicke's aphasia are typically unaware of their errors in speech and do not realize their speech may lack meaning. They typically remain unaware of even their most profound language deficits.
Broca's area, or the Broca area, is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production.
Aphasiology is the study of language impairment usually resulting from brain damage, due to neurovascular accident—hemorrhage, stroke—or associated with a variety of neurodegenerative diseases, including different types of dementia. These specific language deficits, termed aphasias, may be defined as impairments of language production or comprehension that cannot be attributed to trivial causes such as deafness or oral paralysis. A number of aphasias have been described, but two are best known: expressive aphasia and receptive aphasia.
Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neurological disorders; disorders appearing commonly with agraphia are alexia, aphasia, dysarthria, agnosia, acalculia and apraxia. The study of individuals with agraphia may provide more information about the pathways involved in writing, both language related and motoric. Agraphia cannot be directly treated, but individuals can learn techniques to help regain and rehabilitate some of their previous writing abilities. These techniques differ depending on the type of agraphia.
Anomic aphasia is a mild, fluent type of aphasia where individuals have word retrieval failures and cannot express the words they want to say. By contrast, anomia is a deficit of expressive language, and a symptom of all forms of aphasia, but patients whose primary deficit is word retrieval are diagnosed with anomic aphasia. Individuals with aphasia who display anomia can often describe an object in detail and maybe even use hand gestures to demonstrate how the object is used, but cannot find the appropriate word to name the object. Patients with anomic aphasia have relatively preserved speech fluency, repetition, comprehension, and grammatical speech.
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.
Brodmann area 45 (BA45), is part of the frontal cortex in the human brain. It is situated on the lateral surface, inferior to BA9 and adjacent to BA46.
Brodmann area 47, or BA47, is part of the frontal cortex in the human brain. It curves from the lateral surface of the frontal lobe into the ventral (orbital) frontal cortex. It is below areas BA10 and BA45, and beside BA11. This cytoarchitectonic region most closely corresponds to the gyral region the orbital part of inferior frontal gyrus, although these regions are not equivalent. Pars orbitalis is not based on cytoarchitectonic distinctions, and rather is defined according to gross anatomical landmarks. Despite a clear distinction, these two terms are often used liberally in peer-reviewed research journals.
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 Broca's area, which is primarily involved in the production of language. It is traditionally thought to reside in Brodmann area 22, which is located in the superior temporal gyrus in the dominant cerebral hemisphere, which is the left hemisphere in about 95% of right-handed individuals and 70% of left-handed individuals.
Conduction aphasia, also called associative aphasia, is an uncommon form of difficulty in speaking (aphasia). It is caused by damage to the parietal lobe of the brain. An acquired language disorder, it is characterised by intact auditory comprehension, coherent speech production, but poor speech repetition. Affected people are fully capable of understanding what they are hearing, but fail to encode phonological information for production. This deficit is load-sensitive as the person shows significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce. People have frequent errors during spontaneous speech, such as substituting or transposing sounds. They are also aware of their errors and will show significant difficulty correcting them.
The inferior frontal gyrus (IFG),, is the lowest positioned gyrus of the frontal gyri, of the frontal lobe, and is part of the prefrontal cortex.
In neuroanatomy, the arcuate fasciculus is a bundle of axons that generally connects the Broca's area and the Wernicke's area in the brain. It is an association fiber tract connecting caudal temporal cortex and inferior frontal lobe.
Transcortical sensory aphasia (TSA) is a kind of aphasia that involves damage to specific areas of the temporal lobe of the brain, resulting in symptoms such as poor auditory comprehension, relatively intact repetition, and fluent speech with semantic paraphasias present. TSA is a fluent aphasia similar to Wernicke's aphasia, with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia").
In psycholinguistics, 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 same grammatical understanding or systematicity in even human's closest primate relatives.
Brodmann area 22 is a Brodmann's area that is cytoarchitecturally located in the posterior superior temporal gyrus of the brain. In the left cerebral hemisphere, it is one portion of Wernicke's area. The left hemisphere BA22 helps with generation and understanding of individual words. On the right side of the brain, BA22 helps to discriminate pitch and sound intensity, both of which are necessary to perceive melody and prosody. Wernicke's area is active in processing language and consists of the left Brodmann area 22 and Brodmann area 40, the supramarginal gyrus.
Foix–Chavany–Marie syndrome (FCMS), also known as bilateral opercular syndrome, is a neuropathological disorder characterized by paralysis of the facial, tongue, pharynx, and masticatory muscles of the mouth that aid in chewing. The disorder is primarily caused by thrombotic and embolic strokes, which cause a deficiency of oxygen in the brain. As a result, bilateral lesions may form in the junctions between the frontal lobe and temporal lobe, the parietal lobe and cortical lobe, or the subcortical region of the brain. FCMS may also arise from defects existing at birth that may be inherited or nonhereditary. Symptoms of FCMS can be present in a person of any age and it is diagnosed using automatic-voluntary dissociation assessment, psycholinguistic testing, neuropsychological testing, and brain scanning. Treatment for FCMS depends on the onset, as well as on the severity of symptoms, and it involves a multidisciplinary approach.
Paraphasia is a type of language output error commonly associated with aphasia, and characterized by the production of unintended syllables, words, or phrases during the effort to speak. Paraphasic errors are most common in patients with fluent forms of aphasia, and come in three forms: phonemic or literal, neologistic, and verbal. Paraphasias can affect metrical information, segmental information, number of syllables, or both. Some paraphasias preserve the meter without segmentation, and some do the opposite. However, most paraphasias affect both partially.
Neuroscience of multilingualism is the study of multilingualism within the field of neurology. These studies include the representation of different language systems in the brain, the effects of multilingualism on the brain's structural plasticity, aphasia in multilingual individuals, and bimodal bilinguals. Neurological studies of multilingualism are carried out with functional neuroimaging, electrophysiology, and through observation of people who have suffered brain damage.
Sign language refers to any natural language which uses visual gestures produced by the hands and body language to express meaning. The brain's left side is the dominant side utilized for producing and understanding sign language, just as it is for speech. In 1861, Paul Broca studied patients with the ability to understand spoken languages but the inability to produce them. The damaged area was named Broca's area, and located in the left hemisphere’s inferior frontal gyrus. Soon after, in 1874, Carl Wernicke studied patients with the reverse deficits: patients could produce spoken language, but could not comprehend it. The damaged area was named Wernicke's area, and is located in the left hemisphere’s posterior superior temporal gyrus.
↑ Ardila, Alfredo; Bernal, Byron; Rosselli, Monica (2016). "The role of Wernicke's area in language comprehension". Psychology & Neuroscience. 9 (3): 340–343. doi:10.1037/pne0000060. ISSN1983-3288.
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.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
