Cerebral dominance and language

Cerebral dominance and language

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  Cerebral Dominance andLanguage Subhadeep Dutta Gupta
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  Imagine being unableto say, "I am hungry," "I am in pain," "thank you," or "I love you.“ Being trapped inside your body, a body that doesn't respond to commands. Surrounded by people, yet utterly alone. Wishing you could reach out, to connect, to comfort, to participate. For 13 long years, that was my reality. Most of us never think twice about talking, about communicating. I've thought a lot about it. I've had a lot of time to think. --- Martin Pistorius
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  Introduction: • Language iscommunication through words or symbols for words. Language processing is a unique trait of human species • By 6 years of age, children understand about 13,000 words, and by the end of high school, about 60,000 words • It is estimated that 90 % of right – handed persons and 70% of the left – handed persons have a left-hemisphere language specialization
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   Components oflanguage: Phonology: sounds that compose language and the rules that govern their combination. Syntax : rules for combining words into phrases and sentences and determining relations among words. Prosody: contribute to such linguistic functions as intonation, tone, stress, and rhythm (emotional valence).
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  "Babies and childrenare geniuses until age 7 and then there's a systematic decline."
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  • Hemispheric asymmetriesare present in most vertebrates, including fish, amphibians, reptiles, birds and mammals • Recently, lateralization has also been shown in invertebrates, e.g. fruit flies, honeybees or octopuses Concept of Hemispherical lateralization: A structural asymmetry in the Drosophila brain -- Nature 2004;427(6975):605–6.
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  • Functional cerebralasymmetries (FCAs) might have arisen to avoid processing delays deriving from slow interhemispheric transfer, or to prevent interhemispheric conflicts or functional incompatibility • Another long standing hypothesis to explain FCAs is by saving neural capacity due to a reduction of redundant processes • While a specific neural circuit in one hemisphere is processing a specific task, the homologous area in the opposite hemisphere can perform different or complementary processes, allowing a more efficient use of cortical capacity Concept of Hemispherical lateralization: -- Behavioural Brain Research 187 (2008) 297–303
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  Concept of Hemisphericallateralization: -- Cognitive Neuroscience; 3rd Edition
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   Franz JosephGall, Austrian physician and anatomist :  The cortex, forms the basis of mental function  Each mental faculty has its own seat, a circumscribed area of cortex Theory of localization of function  Jean-Baptiste Bouillaud:  In majority of the speech disorder cases, the lesion was localized in the anterior part of the brain The beginning:
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  1. Pathological cases
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  The beginning: A, B: Leborgne’s Brain C, D: Lelong’s Brain -- Brain; (2007) Vol 130 (5) p1432-1441 Pierre Paul Broca (1824-1880) Famous case of ‘Monsieur Tan’
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   Damage/lesion atLeft Inferior Frontal Gyrus:  nonfluent, sparse, dysprosodic, and agrammatical speech Broca’s area ; Broadmann Area 44,45  Broca’s limitation:  Thinking about language as a unitary function localized in a single cortical region
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  One step further…. •Karl Wernicke distinguished between patients who had lost the ability to comprehend language and those who could no longer produce language • Lesion of the posterior and superior temporal lobe on the left hemisphere • such aphasic patients do not understand language • retain the ability to produce utterances with reasonable grammatical and emotional content
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  2. Experimental Techniques
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  Montreal Procedure: • Penfieldand Jasper applied very small electrical charges directly to the cortical surface in epileptic patients. Wilder Penfield and Herbert Jasper Diagram from Penfield’s original study illustrating sites in the left hemisphere at which electrical stimulation interfered with speech
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  Sperry’s Split BrainExperiment -- Neuroscience; 3rd Edition
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  Wada technique -- CognitiveNeuroscience; 3rd Edition
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  3. Brain regionsassociated with language
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  Broca’s Area: • TheIFG is often activated bilaterally but shows left-hemispheric dominance during tasks requiring naming, judgments of phonology, semantics, and syntax • Broca’s region is also activated during acquisition of grammatical rules, discrimination of speech sounds, production of words, estimation of time intervals, and reproduction of rhythms • Thus Broca’s region seems to be involved in both perception and production of speech -- Physiology (2005) 20: 60–69
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  Broca’s Area andthe Mirror Neuron System • Broca’s area : recognition of hand and mouth actions, with recent evidence suggesting a key role in recognizing actions as part of the “mirror” or “observation–execution matching” • Rostral part of the monkey ventral premotor cortex (area F5) is the monkey homolog of Broca's area in the human brain -- Trends Neurosci. 1998 May;21(5):188-94. Orienting behavior Interaction with the external world
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  Broca’s Area: Cerebralasymmetry • Humans have been shown to display left hemisphere dominance of neuropil space and pyramidal neuron dendritic branching in Broca’s region (Schenker et al., 2007) • The cytoarchitectonic areas that comprise Broca’s region (BA44 and BA45) have a greater volume in the left hemisphere as compared with the right in humans (Amunts et al., 1999) -- Physiology, 2005 (20); 60-69
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  Broca’s Aphasia: • Q)What have you been doing in the hospital? “ Yes, sure. Me go, er, uh, P.T. non o’ cot, speech….two times….read….wr….ripe, er, rike, er, write…..practice….get-ting better.” Meaning: “ I go to P.T at one o’ clock to practice speaking reading, and writing and I’m getting better.” -- Case study of David Ford as reported by psychologist Howard Gardner
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  • The hallmarkof Broca’s aphasia is a telegraphic style of speech, in which mainly content words (nouns, verbs, and adjectives carrying content specific to the sentence) are used • Q) Were you in the coast guard? “No, er, yes, yes... ship... Massachu... chusetts... Coastguard... years.” He raised his hands twice, indicating the number “nineteen.” -- Case study of David Ford as reported by psychologist Howard Gardner
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  • The Planumtemporale, is a sheet-like, triangular structure, which lies on the superior surface of the temporal lobe within the Sylvian fissure • Lesion of PT number of associated auditory discrimination and speech comprehension deficits (Caplan and Markis, 1995) Wernicke’s Area: -- J Neurophysiol 2009;101:2725-2732
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  Wernicke’s Area: Cerebralasymmetry
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  -- Brain ResearchReviews 29 (1999) 26–49
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  Wernicke’s Aphasia: • Speakin long sentences that have no meaning, add unnecessary words, and even create made-up words • "You know that smoodle pinkered and that I want to get him round and take care of him like you want before." • Great difficulty understanding speech, and they are often unaware of their mistakes
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  Arcuate Fasciculus • Thearcuate fasciculus is a white-matter fibre tract that links lateral temporal cortex with frontal cortex via a dorsal projection that arches around the Sylvian fissure • On average, the human arcuate fasciculus is larger in the left than the right cerebral hemisphere
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  • The corticalterminations of humans differed from chimpanzees and macaques, with humans having much stronger terminations posteriorly, in the MTG and ITG, as well as anteriorly, in pars opercularis (BA 44), pars triangularis (BA 45), pars orbitalis (BA 47) and surrounding regions • This raises the possibility that the expanded pathway in humans supports the transmission of word-meaning information stored in the MTG and angular gyrus to pars triangularis and orbitalis for both sentence comprehension and sentence construction during spontaneous speech -- Nature Neuroscience (2008) 11, 426 – 428
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  -- Cortex. 2008Sep; 44(8): 953–961 Arcuate Fasciculus: Cerebral asymmetry
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  Language - relatedregions of the left hemisphere mapped by positron emission tomography (PET) in normal human subjects -- Neuroscience (D.Purves), 4th Edn
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  Distribution of 730activation peaks from 129 language studies: top panel – activation peaks for phonological (blue), semantic (red), and syntactic (green) tasks; bottom panel – results of a cluster analysis. -- Neuroimage (2006) 30(4).1414–32.
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  A developmental Magnetoencephalographystudy -- Annu. Rev. Neurosci. (2008);31:511-534.
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  4. Language and Right Hemisphere
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  Evidences: • Some patientswith RH brain damage have subtle deficits in comprehending natural language • Neuroimaging studies often reveal weak neural activities in homologous regions of the RH during language tasks • A growing number of studies report RH greater than LH brain activity while subjects perform higher-level language tasks, such as comprehending metaphors, getting jokes, deriving themes, and drawing inferences, generating the best endings to sentences, mentally repairing grammatical errors, detecting story inconsistencies, and determining narrative event sequences
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  Functions of RHin language: The right hemisphere is involved in processing certain aspects of: • Melody • Prosody, which is the intonation pattern, or sound envelope, of an utterance • Timing • Stress • Pauses • Accent The right hemisphere plays an important role in narrative and inference. Narrative refers to the ability to construct or understand a story line, whereas inference refers to the ability to “fill in the blanks” and make assumptions about material that is not explicitly stated
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  Wernicke- Lictheim’s Housemodel of language
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  Wernicke-Geschwind model:  Serialfashion for language processing.  7 components: • Wernicke’s area • Arcuate fasciculus • Broca’s area • Angular gyrus • Primary auditory Cortex • Primary visual cortex • Primary motor cortex
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  Primary Auditory Cortex:Primary Visual Cortex: Reception of auditory stimulus Reception of visual stimulus Angular Gyrus: Shape of the symbols Wernicke’s Area: Interpretation of the words and meaning given Arcuate Fasciculus: Information transmission Broca’s Area: activates the appropriate response to the word Primary Motor Cortex: Vocalization
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  Tripartite organization forlanguage system 1. Language Implementation System: Broca’s area, Wernicke’s area, parts of insular cortex and Basal Ganglia -- Decodes incoming verbal information and produces appropriate verbal responses 2. Language Mediation System: Association cortex in the temporal, parietal and frontal lobes 3. Language Conceptual System: higher level association cortex areas -- Damasio and Damasio, 1992
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  Dual Stream Modelof Language Processing  A/c to this model, there are two functionally distinct computational/neural networks that process language information: • one that interfaces sensory/phonological networks with conceptual-semantic systems, and • one that interfaces sensory/phonological networks with motor-articulatory systems -- Nature Neuroscience, 2007 (8) 393-402
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  Left hemisphere biasness– Why?? Incorporation of vocalization: Vocalization itself, appears to be left-hemispheric even in nonhuman species, from frogs (Bauer, 1993) to mice (Ehert, 1987) to primates (Hook-Costigan & Rogers, 1998), leading Corballis (2003) to propose that it was the incorporation of vocalization into the human mirror system that extended the left-hemispheric bias to the cortical level, giving rise perhaps to nonlinguistic asymmetries such as the left-hemispheric dominance in manual praxis—and indeed the phenomenon of right-handedness itself.
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  4. Language Asymmetry and Genetics
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  FOXP2 • Forkhead boxP2 (FOXP2) gene – in the long arm of chromosome 7 (7q31) • Study of British K.E family:  Across 3 generations, 15 out of 37 members suffered from ‘Verbal dyspraxia’ - orofacial movement disorder  Autosomal dominant mutation  Substituted a histidine for an arginine at site 553 in the FOXP2 sequence
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  Inferior frontal Basal Ganglialoop Inferior frontal – cerebellum loop -- Nature Reviews Neuroscience (2005) 6; 131-138
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  Lateralization of geneexpression in human language cortex Data from Pletikos et al, 2014) Data from Hawrylycz et al,2012). Box plots of STG lateralization t-statistics, for genes within the four most significantly lateralized gene sets in meta-analysis, and an additional non-lateralized gene set (metallopeptidase activity) for comparison. -- Cortex (2015) 67; 30–36
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  Large & diffused semanticfields Small & focused semantic fields Multiple distantly related words Coarse interpretation Summation of weak activation
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  Bicêtre Hospital, theplace of Leborgne's illness. -- Credit: National Library of France.
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  We’ve come along way from the days of phrenology. And much of it is thanks to the man who couldn’t speak—and the doctor who understood just how meaningful that loss would be for the future of science.