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International Journal of Health Sciences and Research www.ijhsr.org ISSN: 2249-9571

Review Article

Neurobiology of Language Development: An Update

Vikas Kumar1, Joydeep Das2, Madhumita Bhattacharya3

1Clinical Psychologist, Sri Sri University, Cuttack, Odisha. 2PhD. Scholar, Dept. of Clinical , Central Institute of Psychiatry, Kanke, Ranchi, Jharkhand. 3Assistant Professor, Dept. of Clinical Psychology, Central Institute of Psychiatry, Kanke, Ranchi, Jharkhand.

Corresponding Author: Vikas Kumar

ABSTRACT

Language is a human‟s ability to use an extremely rich set of symbols, plus rule for combining them to communicate information. The concept of the emerging field of neurobiology of language is that foremost study of the human brain, i.e., it is a subfield of neuroscience and particular in human neuroscience. By saying this, we mean to distinguish this from this related field psychology and , in which the emphases of investigation are certainly to understanding the brain but are not ispo facto focused on the understanding of neural mechanism. The human brain has multiple anatomical specializations that may be relevant to explaining our capacity for language. First, human brains have wider cortical minicolumns in both Broca‟s and Wernicke‟s areas compared with great apes. Second, human brains exhibit leftward asymmetries in Broca‟s area volume and in the width of planum temporal minicolumns that are not found in great apes. Third, the projections of the human arcuate fasciculus reach beyond Wernicke‟s area to a region of expanded association cortex in the middle and inferior temporal cortex that appears to be involved in processing word meaning.

Keywords: Language Development, Neurobiology of Language, Broca’s areas, Wernicke’s areas, and psychiatric disorders.

INTRODUCTION The language of human What is language: Language is human‟s being is thus one of the most interesting and ability to use an extremely rich set of significant evolutionary events that which symbols, plus rule for combining them to has occurred in the last 5–10 million years, communicate information. The human and indeed during the entire history of life ability to use language far exceeds that any on Earth. Given its central role in human other organism on earth. As Bhartrihari, an behavior, and in human culture, it is Indian thinker observed „Everything is unsurprising that the has cognized through language‟. Indeed, been a topic of myth and speculation since language changes the world of experience in before the beginning of history. From the critical ways. Language is a unique power dawn of modern evolutionary theory, of bestowed human to represent and share Darwin questions about the evolution of unbounded thoughts is critical to all human language have generated a rapidly growing societies and has significantly played a scientific literature. Since the 1960s, an pivotal role in the rise of human as species increasing number of scholars with in the last million years from peripheral and backgrounds in genetics, anthropology, a minor member of the sub-Saharan African science linguistics, neuroscience, ecological community to the dominant and and devoted species on the earth today.

International Journal of Health Sciences & Research (www.ijhsr.org) 256 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update themselves to understand various aspects of described six characteristics of language: language evolution and language sciences. The signals used are 1) vocal; 2) articulate, Language from Apes to Humans: that is complex sounds are constructed from Mutation of the FOXP2 gene need phonetic units; 3) have a conventional not have been the only factor in the switch. meaning (to the speaker and recipient); 4) Until the emergence of Homo sapiens, the the sounds are indicative (or represent anatomical requirements for fully articulate objects or events in the environment); 5) speech were probably not complete. For they are produced with the intention of example, the hypoglossal canal is much communicating to someone else; and 6) they larger in humans than in great apes, are joined together to form new suggesting that the hypoglossal nerve, combinations. Bierens de Haan concluded which innervates the tongue, is also much that although animals meet the first five larger in humans, perhaps reflecting the criteria: “real creative language, the faculty importance of tongued in speech of combining words into phrases, is beyond (Corballis, M. C., 2009). The evidence the faculties of the animal mind. It is only suggests that the size of the hypoglossal the human mind that possesses the full canal in early australopithecines, and faculty of combining words into phrases and perhaps in Homo habilis, was within the phrases into conversations, of constantly range of that in modern great apes, while creating new means to express and that of the Neandertal and early Homo communicate feelings and thought sapiens skulls was contained well within the (Snowdon, C. T., 1990). modern human range. A further clue comes The accomplishments of apes, from the finding that the thoracic region of monkeys, and birds do not approach those the spinal cord is relatively larger in humans of a human child. However, it would be than in nonhuman primates, probably naive to expect an ape to match totally the because breathing during speech involves linguistic competence of a human child. extra muscles of the thorax and abdomen Bonobos, chimpanzees, and humans are (Corballis, 2009). distinct species, each of which has evolved Animals models for language: its own communicative and cognitive Human beings are unique in that adaptations. Among the defining they communicate through a system of characteristics of our own species are our language. Non-human animals have a linguistic and cognitive skills. If we were to system of communication but lack language. find a Kanzi that imitated all human Thus, a nonhuman animal might be able to cognitive and linguistic abilities, we would signal food or danger or make sexual probably be asking ourselves what sort of advances to another animal but is not able to genetic disorder led him to be so short and produce language akin to ours. However, hairy. The finding of some rudiments of many species share with us mechanisms for language-like phenomena in natural sound production. Zebra finches share many communication, such as simple , features with human beings pertaining to rudimentary symbolization, similar communication and sound production. Both perceptual systems, along with the potential have critical periods during development exhibited by some of the great apes, during which they must hear the sounds of indicates that many of the components of their respective communication or language linguistic ability have appeared at different they are to produce, and both have specific times in evolution; but it is only with human temporal periods during which they must beings that all of the components that define hear as well as practice these sounds our linguistic abilities have come together in (Helekar et. al., 2003). one species. Bierens de Haan, one of the earliest reviews of animal language parallels,

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Prenatal language learning: provides a basis for Prenatal language learning is an constructing a large and expandable set important aspect of human development. of words out of two or three dozen During the third trimester of gestation, a phonemes. A phoneme is the basic unit baby in the womb can hear the mother's of sound in a language; it is the smallest voice clearly and makes use of this ability unit of sound that affects meaning. by learning the rhythms, tones, and  refers to the units of sequences of whatever languages the mother meaning involved in word formation. A speaks. These phonological patterns do not is a minimal unit of meaning; stand apart from context but instead, are it is a word or a part of a word that experienced as integral parts of the mother's cannot be broken into smaller moods and activities. By building up neural meaningful parts. patterns in the brain, the baby gets a head  involves the way words are start on the phonological contours, combined to form acceptable phrases grammars, and uses of the mother's and sentences. languages (Childs, M. R., 1998).  refers to the meaning of Babies begin learning the language words and sentences. Every word has a in the womb. An early discovery using set of semantic features, which are acoustic spectrography revealed that the required attributes related to meaning. first cry of a 900-gram baby already Words have semantic restrictions on contained intonations, rhythms, and other how they can be used in sentences. speech features that could be matched with  system of using appropriate the mother's voice spectrograph. This conversation and knowledge of how to proved that by about 26 weeks of gestation, effectively use language in context. this baby had already acquired certain features of its mother tongue (Sherr, L., Neurobiological origins of language: 1995). Language has a long evolutionary Communication in the antenatal period: history and is closely related to the brain,  Unborn babies can recognize their but what makes the human brain uniquely mum's voice from 16 weeks and dad's adapted to language is unclear. The regions from 20 weeks of the brain that are involved in language in  Unborn babies respond to singing and humans have similar analogues in apes and being read to from 24 weeks. They may monkeys, and yet they do not use language. move about to show that There may also be a genetic component;  They are listening, babies develop mutations in the FOXP2 gene in humans, preferences for music while in the womb the gene that prevents from constructing and they can move in rhythm to music complete sentences (Arbib, M. A., 2005). and their heart rate increases Neurobiology of language development:  Babies are able to remember from the The study of the relation of brain to first trimester and babies communicate language functioning is called through movement all the way through . Lenneberg (1967) pregnancy hypothesized that the two hemispheres are  It is really important to communicate equipotential for language until and stimulate a baby right from the start. approximately two years of age, at which Structure of Language / The rule system time Left Hemisphere dominance begins to of Language: develop and continues until puberty. This  Phonology is the sound system of the neural basis is stable across languages like language, including the sounds that are Chinese, English, Hindi and many sign used and how they may be combined languages, i.e. the left-lateralized network of (Stoel-Gammonand Menn, 2009). the brain is dominant (Mac Sweeney, et. al.,

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2008). The newer studies suggest, for perisylvian association cortex to example, that there is not one unified components of the language processing language area in the brain where linguistic system have been developed. One is based signals are processed. Different brain on holist or distributed views of neural systems sub serves different aspects of function and one on localizationist language processing, and the language principles. The basic tenet of processing areas of the brain include many holist/distributed theories is that linguistic more regions than the classicalBroca‟s and representations are distributed widely and Wernicke‟s areas (Zatorre et. al., 1992). that language processing components rely There is evidence that the language system on broad areas of the association cortex. is more flexible during development than Localizationist theories maintain that later in life. For example, damage to classic language processing components are left hemisphere language regions, especially localized in specific parts of the cortex the Broca‟s area () and (Ojemann, 1991). Wernicke‟s area (speech comprehension) during development have much less Neurobiological adaptations for pronounced effects on language abilities language: than damage to the same brain regions in Broca's and Wernicke's areas: adulthood (Bates, 1999). The gene These regions are where language is responsible for language impairments is located in the brain everything from speech localized to the long arm of chromosome 7 to and writing. The language itself in the 7q31 region and subsequently is based on symbols used to represent identified as the FOXP2 gene. The concepts in the world and this system significant linkage has been reported to appears to be housed in these areas. The 13q21 (using various language phenotypes), language regions in human brains highly 16q (using a phonologic memory resemble similar regions in other primates, phenotype), and 19q (again, with various even though humans are the only species phenotypes) (Feldman, 2007). that use language. The Neurobiology of Language The brain structures of chimpanzees Processing: are very similar to those of humans. Both Language processing subdivides contain Broca's and Wernicke's homologues functions such as reading, speaking, that are involved in communication. Broca's auditory comprehension, and writing into area is largely used for planning and many different, semi-independent producing vocalizations in both components, which are sometimes called chimpanzees and humans. Wernicke's area modules or processors. These components appears to be where linguistic can be further divided into variable numbers representations and symbols are mapped to of highly specialized operations, such as specific concepts. This functionality is those involved in mapping features of the present in both chimps and humans; the acoustic signal onto phonemes or in chimp Wernicke's area is much more similar constructing syntactic structures from to its human counterpart that is the Broca's words. Each operation accepts only area, suggesting that Wernicke's is more particular types of representations as input evolutionarily ancient than Broca's and produces only specific types of (Taglialatela, et. al., 2008). representations as output (Temple, C., Connections between Wernicke’s and 2014). Broca’s areas: The perisylvian cortex organized to Beyond these human specializations support these functions has been the subject within human Broca‟s and Wernicke‟s of much investigation. Two general classes areas, there are differences between humans of theories of the relationship of parts of the and non-human primates in the white-matter

International Journal of Health Sciences & Research (www.ijhsr.org) 259 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update connections that link these two regions. activation patterns in the Broca's area of Anterograde and retrograde tracer both humans and monkeys. When monkeys techniques have been used to describe the view other monkeys gesturing, mirror connections of Wernicke‟s and Broca‟s neurons in the Broca's homologue activate. areas homologues in macaque monkeys. Groups of mirror neurons are specialized to Direct connections between the two regions respond only to one kind of viewed action, have been identified, but the pathway is and it is currently believed that these may be weak and its function unknown. In fact, the an evolutionary origin to the neurons that dominant frontal connection of Wernicke‟s are adapted for speech processing and homologue (area Tpt) is not within the production. process; it is displaced from nearby Other regions involved in language: extrastriate visual cortex (Rilling, J. K. Cortical areas in the vicinity of 2014). For example, visual motion area MT Broca‟s and Wernicke‟s regions, other brain lies within the superior temporal sulcus areas participate in language processing as (STS) in chimpanzees and rhesus macaques. well, for example, the motor cortex. Their However, in humans, it lies considerably role in speech function such as articulation posterior to STS, and STS instead appears to has been demonstrated in contain association cortex. The posterior electrophysiological studies of Foerster and limit of the temporal-lobe arcuate fasciculus the Vogts at the beginning of the twentieth terminations in the human brain coincides century. The involvement of the premotor very closely with the anterior limit of visual cortex in language processing has been motion area MT, consistent with a elucidated by recent functional imaging displacement of MT by the highly expanded techniques, but also intraoperative mapping arcuate pathway. in patients during neurosurgery. It has been Motor neurons: hypothesized, that the premotor cortex plays In order to speak, the breathing a role in the planning but also in semantic system must be voluntarily repurposed to processes and categorization. produce vocal sounds, which allows the The dorsolateral prefrontal cortex, breathing mechanisms to be temporarily frontal operculum, and the insula participate deactivated in prefer of song or speech in different aspects of language processing, production. The human vocal tract has and so forth. A complete list of cortical evolved to be more suited to speaking, with areas involved in language would a lower larynx, 90° turn in the windpipe, encompass areas of even more cortical and large, round tongue. Motor neurons in regions. Subcortical nuclei, for example, the birds and humans bypass the unconscious basal ganglia and the thalamus, participate systems in the brainstem to give direct in language processing as well. Finally, an control of the larynx to the brain. important aspect of speech control is the Gestural origin: neuromuscular control of tongue, lips, The earliest language was strictly larynx, pharynx, the vocal cords and the vocal, reading and writing came later. Some muscles necessary for breath and so forth, new research (Arbib, M. A., Liebal, K., and which are controlled, in addition to cortical Pika, S. 2008) suggests that the combination motor and somatosensory areas, by the of gestures and vocalizations may have cerebellum and cranial nerves and their moderated to the development of more nuclei (Binder et. al., 1997). complicated language in protohumans. The cerebellum also has increased Chimps that produce attention-getting its rCBF in some activation studies sounds show activation in areas of the brain involving both language and other cognitive that are highly similar to Broca's area in functions. This may be a result of the role of humans. Even hand and mouth movements this part of the brain in processes involved with no vocalizations cause very similar in timing and temporal ordering of events,

International Journal of Health Sciences & Research (www.ijhsr.org) 260 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update or in its being directly involved in language mapping of letter symbols or phonemes onto and other cognitive functions (Andreasen et. a word lexicon and, finally, semantic access al., 1998). and integration. The fact that the same Development of language and plasticity: semantic knowledge can be accessed by Evidence for the plasticity of symbols in two different modalities allows language in the human brain should not be exploration of the brain substrate that surprising in light of all that has been underlies retrieval of supramodal meaning learned in the last few decades about (Marinkovic et. al., 2003). developmental plasticity of isocortex in Evidence from functional brain other species (Bates, E., 1999). imaging suggests that language Children with left or right focal brain comprehension is subserved by modality- injuries should yield the strongest evidence specific distributed networks (Cabeza and for plasticity because these children acquire Nyberg, 2000). , as well as their lesions before language development complex non speech stimuli, evoke bilateral has gotten underway. At the same time, this activation in the superior temporal is the period of development in which cortices (Binder et al. 1997, and Zatorre et. inherent regional specialization should be al. 1992). Leftward speech-related most apparent because the child has not yet asymmetry has been observed in temporal had the time or occasion to develop and left inferior prefrontal cortex (Friederici alternative forms of brain organization et. al. 2000, Price et al. 1997). (Bates et. al., 1997). Neuroimaging studies of reading, however, Thus, a focal lesion within the left suggest a more clearly left lateralized hemisphere may result in an initial delay in activity in ventral temporal and inferior the first stages of linguistic development, in prefrontal regions (Gabrieli et. al. 1998). comparison with normal children and in The available neuroimaging evidence children with early right hemisphere suggests that the prefrontal and temporal damage. Subsequently, however, the neural regions contribute to semantic and and behavioral plasticity of the developing mnemonic processing of words presented in brain may permit undamaged cerebral areas both spoken and written and may represent to solve the linguistic task, resulting in the neural basis of supramodal processing. performance that is well within the normal Hickok and Poeppel (2007) have suggested range. that language is represented by two An enduring issue in the processing streams: neurobiology of language concerns the (1) a bilaterally organized ventral stream, origins of the specialized role of language which is involved in mapping sound onto areas within the left hemisphere and meaning and includes structures in the whether they arise from a specialization superior and middle portions of the temporal specifically for the processing of linguistic lobe; and information, or whether they are linked to (2) a left dominant dorsal stream, which more general aspects of processing, such as translates acoustic speech signals into motor the sensory and motor information representations of speech and includes the important in speech perception and posterior frontal lobe and the dorsal-most production (Gazzaniga, 2000). aspect of the temporal lobe as well as the Word processing: parietal operculum. Human interaction and thought Focusing on the ventral stream, crucially depend on words, which can take Hickok and Poeppel propose a model which either auditory or visual form. During initial suggests that cortical speech processing first word processing stages, the acoustic signal involves the spectrotemporal analysis of the or letter string are analyzed in their acoustic signal by auditory cortices in the respective sensory modalities, followed by dorsal superior temporal gyrus (STG) and

International Journal of Health Sciences & Research (www.ijhsr.org) 261 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update phonological level processing involves the Language comprehension involves middle to posterior portions of the superior processes at multiple levels of analysis temporal sulcus (STS). Subsequently, the including lexical, syntactic, semantic, and system diverges in parallel into the ventral pragmatic & discourse. Research on and dorsal streams. The ventral stream individuals with brain damage has led to the projects toward the posterior middle and realization that both cerebral hemispheres inferior portions of the temporal lobes, a are involved in language comprehension, region believed to link phonological and albeit to varying degrees with regard to semantic information. These authors argue these different levels of linguistic analysis that the more anterior regions of the middle (Caplan, 1992). Discourse processes as they and inferior portions of the middle temporal are an integral part of our daily gyrus (MTG) are involved in a communications, subsuming, but also going combinatorial network of speech beyond, the processes engaged in processing. recognizing words, syntactic parsing and Sentence processing: comprehending isolated sentences Listening to connected speech is a (Gernsbacher, 1994). task that humans perform effortlessly each A person with right hemisphere day. This is surprising given the short time damage is often described as experiencing that the processing system has to deal with difficulties at the level of discourse. They different types of information. Segmental tend not to elaborate on details of a phonemes and suprasegmental phonological discourse, producing fewer propositions and information (prosody or pitch), as well as fewer complex propositions, although their syntactic and semantic information, must be basic knowledge of scripts or event schema accessed and coordinated within appears to be intact. Right hemisphere milliseconds. damage patients are frequently unable to The functional neuroanatomy of maintain the theme of a conversation, speech perception prior to syntactic and missing the main point altogether (Brownell semantic processes has been described in and Martino, 1998). Right hemisphere detail recently by Hickok and Poeppel damage patients have been found to have (2007). Studies on the functional difficulties drawing certain types of neuroanatomy of semantic processes at the inferences (Beeman, 1993) or revising them sentence level are rare. Rather, most when new information comes up in a imaging studies of semantic processes are discourse (Bihrle et. al., 1986). conducted at the word level. Such studies Conceptual semantic knowledge: indicate that the left middle temporal gyrus The semantic system necessarily (MTG), the angular gyrus and the left involves impairment in comprehension and inferior frontal gyrus (IFG) support production of spoken and written words. semantic processes. It is proposed that the Currently, the internal organization of the frontal cortex is responsible for the strategic semantic system has been a subject of much and executive aspects of semantic debate; a widely accepted opinion is that processing. Friederici (2002)studies meaning is represented as a set of semantic investigating semantic processes at the features and that the semantic information sentence level report a variety of activation associated with an object can be accessed loci, including the left IFG (Brodmann area, from both pictures and words. This has an BA 45/47), the right superior temporal important consequence for rehabilitation gyrus (STG) and the left MTG, as well as since to address the semantic system the left posterior temporal region. Anterior language is not required. Pictures, compared and posterior temporal activation has been to words, have a privileged access to the reported during sentence processing. semantic system because they represent Discourse processing & pragmatics: directly some of the semantic features of the

International Journal of Health Sciences & Research (www.ijhsr.org) 262 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update corresponding concept whereas the capacity limited system that comprises a relationship between a word and its meaning controlling central executive and that is arbitrary. includes an articulatory loop system. The The way in which we interact with central executive, the component that is not the world is determined by our network of well understood, is thought to regulate accumulated knowledge concerning the information flow within working memory, objects, animals, and people that comprise retrieval of information from other memory it. The organization of this conceptual systems, and the processing and storage of database, typically termed semantic information. The articulatory loop, the memory, remains a much-debated issue. better-understood component, includes a Neuropsychological studies of brain- capacity limited phonological short-term damaged individuals with disrupted store and an articulatory control process semantic memory, and more recently, (verbal rehearsal) that acts to refresh and functional imaging investigations in healthy maintain speech material in the store for a control subjects, have been critical in brief period. The articulatory loop‟s shaping current theories regarding the function is to store verbal input temporarily, cognitive and neural architecture of this especially novel phonological input, while system (Thompson et. al., 2004). other cognitive tasks such as auditory The neural basis of general semantic comprehension take place. The ability to memory has been extensively investigated, temporarily store novel material also allows and it is generally accepted that regions the listener the opportunity to create long- within the left temporal lobe are critically term phonological representations of that involved in the representation of knowledge material (Baddeley et. al., 1998),this view of for objects and animals (Wiggs et. al., working memory will hereafter be referred 1999). The literature related to personal to as phonological working memory knowledge, however, reveals a major (PWM). discrepancy between brain regions Universal : implicated by neuropsychological case The language bioprogram hypothesis reports and regions suggested by functional proposes that humans have an innate, imaging studies. The majority of cases who cognitive grammatical structure allowing have presented with impairments in person- them to develop and understand language. specific semantics have had right temporal According to this theory, this system is lobe damage. embedded in human genetics and underpins A person with semantic dementia, a the basic grammar of all languages. Some neurodegenerative condition which affects evidence suggests that at least some of our anterior and infero-lateral regions of the linguistic capacities may be genetically temporal lobe, provide a unique opportunity controlled. Mutations in the FOXP2 gene to investigate the psychological and neural prevent people from combining words and basis of conceptual knowledge. Despite a phrases into sentences. However, these profound loss of semantic knowledge with genes are present in the heart, lungs, and anomia and impaired comprehension, many brain, and their role is not entirely clear other cognitive processes including (Locke, J. L., and Bogin, B. 2006). phonological and syntactic aspects of Brain areas associated with language language, working memory, non-verbal during different stages of Development: problem solving, visuospatial and frontal In most of the adults, the left executive function are preserved, at least in hemisphere of the brain is dominant for the early stages of the disease. language that is language function is Memory for language: lateralized. When it comes to language, the Working memory according left hemisphere is primarily characterized to Baddeley (1986) is a multicomponent, by a capacity to analyze and sequence

International Journal of Health Sciences & Research (www.ijhsr.org) 263 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update linguistic information, while the right (Dick et. al., 2008). The hemisphere is known for its holistic area of Rolando, located in the precentral perception. Right-hemispheric damage often gyrus at the Rolandic fissure, which is the results in problems with social primary motor area involved in the motor communication, also referred to as control of the speech act, while the pragmatics. Locke argued, in his theory of secondary motor area for initiating speech language development, that the right motor activity adjacent to it overlaps partly hemisphere sub-serves language with Broca‟s area. The during the first two phases, encoding is considered to be localized in the when the child is oriented towards perisylvian region, near the Sylvian fissure, interaction with the caregiver and the of the dominant hemisphere, while collecting of whole utterances (Locke, articulatory retrieval is located in Broca‟s 1997). The left hemisphere gradually takes area (Baddeley et. al., 1998). Hickok and command, as the child starts to analyze the Poeppel proposed a dual-stream model of different elements of language and the rules speech processing involving auditory fields for their combinations. In this way, of the superior temporal gyrus bilaterally language lateralization develops. The fMRI (Hickok and Poeppel, 2007). A ventral studies suggest that early language stream processes speech signals for processing is predominantly bilateral (Dick comprehension projects towards the inferior et. al., 2008). The occurrence of posterior temporal cortex and is largely lateralization is taken about one year earlier bilateral. in girls than in boys, which corresponds The dorsal stream maps sound onto with the earlier onset of puberty in girls. In articulatory-based representations involves a children with brain damage, cognitive region in the posterior Sylvian fissure at the functions can be shifted to other brain parietal-temporal boundary and ultimately regions, as for language, to the non- projects to the frontal regions. It is strongly dominant and most often the right left-hemisphere dominant. A memory hemisphere. The possibility of brain repair, network within the limbic system, including called plasticity, is more likely to occur the hippocampus, interacts with speech and before lateralization is completed (Carlsson, language, as the left hippocampus is 1994). particularly important for memory for The areas of the brain mainly language. Moreover, associative areas involved in language processing for within several regions in the temporal, receptive language are Wernicke‟s area frontal and parietal lobes interact with the located in the posterior part of the temporal main language system (Mesulam, 1990). lobe and adjoining parts of the parietal lobe, The cerebellum is associated primarily with adjacent to the auditory cortex, and for the balance and coordination of movements, expressive language are Broca‟s are located but it has lately also been associated with in the lower posterior part of the frontal language functions, particularly with the lobe. The structures those which are modulation of linguistic and other cognitive integrated into a network and form a abilities and with motor speech planning. language implementary system. In Cerebral asymmetry of language: childhood, these areas gradually increase in The language function shows functional thickness, corresponding to increased grey laterality towards the left side of the brain. matter (Dick et. al., 2008). This results in an This function of language largely depends asymmetry between the hemispheres, where on the posterior area of superior temporal the left hemisphere is larger than the right, gyrus. Damage to this area is associated particularly in the area of the planum with a defect in comprehension of spoken temporal. Reversed or absent asymmetry language. It is considered that the specific has been seen in studies of children with area is responsible for language function

International Journal of Health Sciences & Research (www.ijhsr.org) 264 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update and it is named as Wernicke‟s area. Split- Alzheimer's disease: The left hemispheric brain patients were capable of naming damage is linked to problems with semantic objects when presented to the left memory and language, so someone may hemisphere but failed to do the same task struggle to find the right word for when presented to the right hemisphere, something. Recent studies of persons with proving a major left hemisphere neurological impairment implicate a right involvement in language function. hemisphere-subcortical circuit in the Neurobiology of language development in production of formulaic expressions (Van different disorders: Lancker Sidtis, 2012). In AD clinical Aphasia: Primary progressive aphasia observations point strongly to preserved (PPA), normally resulting from a production of formulaic expressions which, neurodegenerative disease such as when unrecognized, may mask veridical frontotemporal dementia or Pick Complex cognitive and language deficiencies. or Alzheimer‟s disease and it is : Disorder marked heterogeneous clinical condition indicating abnormalities involve in the acquisition and by a progressive loss of specific language pragmatic language skills among 25-50% of functions with giving initial caution of other individuals with the diagnosis (Rapinand cognitive domains. Dunn, 2003) and rest of the 50-75% have a Neuroimaging in aphasia: Neuro-imaging failure to develop language skills at any studies reveal that majority of PPA patients level. As the severity of the disorder varies, represent with structural and metabolic language abilities in children with ASD changes limited to their dominant language range anywhere from nearly normal to hemisphere, especially in the area of the left profoundly impaired. Individuals of Sylvian fissure (Caselli and Jack 1992; Nonverbal with ASD are a distinct minority Gorno- Tempini et. al. 2004, 2008; in research reports, as because an Mesulam 2003; Mesulam et. al., 2008). The understanding of communicative specific, abnormalities in the left posterior impairments is hoped to lead to an frontoinsular region, i.e. inferior frontal understanding of failed communicative gyrus (Broca area), insula, premotor and skills. supplementary motor areas have been Brain imaging studies of language in usually detected in patients with apraxia of ASD: speech and agrammatism (Hu et al. 2010; Several studies have been done to Nestor et al. 2003; 2008; Rohrer et al. 2008; investigate language processing in ASD Whitwell et al. 2010). Nonetheless, some using functional brain imaging. In one study individuals with this variant have been of fMRI of adults with ASD, an abnormal shown to have more generalized atrophy language-related responses found in Broca‟s (Cappa et. al., 1996), and there is a subset of area (left inferior prefrontal cortex, BA45) cases with unremarkable imaging (Mesulam and left middle temporal gyrus (BA21) et. al. 2008). during “deep” (semantic) vs. “shallow” Dementia: (perceptual) processing of visually Dementia is caused when the brain is presented words (Harris, et. al., 2006). The damaged by diseases, such as a series of subjects of ASD also showed diminished strokes or Alzheimer‟s disease. The disease activation to concrete versus abstract words. of Alzheimer‟s is the most common cause A consistent Data with the possibility that of dementia but not all dementia is due to participants with ASD were performing Alzheimer‟s. The specific symptoms that more semantic and phonological processing someone with dementia experiences will during perceptual tasks, and were thus less depend on the specific location of the brain able to suppress this processing. In a related which is damaged and the disease that is semantic category task, a small sample of causing dementia. adults with autism was compared to

International Journal of Health Sciences & Research (www.ijhsr.org) 265 Vol.9; Issue: 1; January 2019 Vikas Kumar et.al. Neurobiology of Language Development: An Update matched controls on the ability to categorize with activation in the right posterior middle a set of words as tools, colors, or feelings temporal lobe (left Brodmann's area 22) and (Gaffrey, M. S., et. al., 2007). The group of left superior frontal gyrus (left Brodmann's autism had less activation of left inferior area 10) in controls but not in people with frontal gyrus (Broca‟s area) than controls, schizophrenia and postulated that this might but more activation in visual areas contribute to their simpler speech patterns. (extrastriate visual cortex bilaterally), suggesting an important role of perceptual CONCLUSION components (possibly visual imagery) The evolution of human language is during semantic decision. In language- suggested that “it the hardest problem in related activity in Lateralization (which science” (Christiansen and Kirby, 2003) and hemisphere of the brain) of language some of the skeptics have credibly functioning in ASD has been shown to be concluded that scientists might spend their aberrant in multiple studies. time more constructively on more tractable Schizophrenia: In Schizophrenia deficit in topics (Lewontin, 1998). Language has not verbal functioning showing various been fossilizing, and we lack time machines, abnormalities in aspects of verbal so all of our data are indirect, and often production and an extensive literature exist, several steps removed from the direct, comprehension and cerebral lateralization conclusive evidence we might desire. But for language (DeLisi L. E., 2001).Some this is true of many problems in science that epidemiological and clinical reports indicate are considered legitimate pursuits, from the that language abnormality in people with Big Bang to the origin of life, so this schizophrenia may predate the illness and difficulty is not insuperable. A biological have their origins in early brain understanding of language would surely development, as evidenced by noted delays entail a full understanding of how brains in and reading abilities generate, represent, and manipulate (DeLisi L. E., et. al., 1991., Henriksson KM, concepts, and such a broad understanding of McNeil TF., 2004). cognitive neuroscience remains a distant Functional studies of language processing hope today to understand the neurobiology in Schizophrenia: of language & language development (some Several fMRI studies using language pessimistically suggest it is forever beyond paradigms also show abnormal processing the reach of the human mind. on verbal fluency tasks and loss of left hemisphere lateralization in the temporal REFERENCES and frontal lobes of patients with chronic  Andreasen, N. C., Paradiso, S., &O'leary, D. schizophrenia (Sommer I.E.C., Ramsey NE, S. (1998). “Cognitive dysmetria” as an Kahn RS.,2001; Kubicki M, McCarley RW, integrative theory of schizophrenia: a and Nestor PG, et. al., 2003). dysfunction in cortical-subcortical- Recent fMRI studies provoke cerebellar circuitry? Schizophrenia activation with various language paradigms Bulletin, 24(2), 203-218.  Arbib, M. A. (2005). From monkey-like in patients who already have the diagnosis action recognition to human language: An of schizophrenia and provide evidence for evolutionary framework for disturbances in the representation and neurolinguistics. Behavioral and brain processing of meaning of words, text, sciences, 28(02), 105-124. discourse and verbal self-  Arbib, M. A., Liebal, K., &Pika, S. (2008). monitoring (Boksman K, et. al.,2005;Weiss Primate vocalization, , and the E.M, et. al., 2006; Yurgelun-Todd D. A., et. evolution of human language. Current al., 1996;Fu C. H., et. al.,2006; Kircher, et. Anthropology, 49(6), 1053-1076. al. 2002) showed that the number of  Baddeley, A. (1986). Working memory and complex sentences produced was correlated comprehension. In D. Broadbent, J.

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