Cerebral dominance and language

The presentation focuses on cerebral asymmetries in structural, functional and molecular levels regarding production and comprehension of language faculty. It also briefs about the role of different language areas and sex differences in language.

1. Cerebral Dominance and Language Subhadeep Dutta Gupta

2. Imagine being unable to 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

3. Introduction: Language is communication 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

4. Components of language: 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). 

5. "Babies and children are geniuses until age 7 and then there's a systematic decline."  

6. Hemispheric asymmetries are 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.

7. Functional cerebral asymmetries (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

8. Concept of Hemispherical lateralization: -- Cognitive Neuroscience; 3 rd Edition

9. Franz Joseph Gall , Austrian physician and anatomist : The cortex, forms the basis of mental function E ach 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:

10. 1. Pathological cases

11. 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’

12. Damage/lesion at Left 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

13. 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

14. 2 . Experimental Techniques

15. Montreal Procedure: Penfield and 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

16. Sperry’s Split Brain Experiment -- Neuroscience; 3 rd Edition

17. Wada technique -- Cognitive Neuroscience; 3 rd Edition

18. 3. Brain regions associated with language

19. Broca’s Area: The IFG 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

20. Broca’s Area and the 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

21. Broca’s Area: Cerebral asymmetry 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

22. 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

23. The hallmark of 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

24. The  Planum temporale , 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

25. Wernicke’s Area: Cerebral asymmetry

26. -- Brain Research Reviews 29 (1999) 26–49

27. Wernicke’s Aphasia: Speak in 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

28. Arcuate Fasciculus The arcuate 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

29. The cortical terminations 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

30. -- Cortex. 2008 Sep; 44(8): 953–961 Arcuate Fasciculus: Cerebral asymmetry

31. Language - related regions of the left hemisphere mapped by positron emission tomography (PET) in normal human subjects -- Neuroscience ( D.Purves ), 4 th Edn

32. Distribution of 730 activation 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 .

33. A developmental Magnetoencephalography study -- Annu . Rev. Neurosci . (2008);31:511-534.

34. 4 . Language and Right Hemisphere  

35. Evidences : Some patients with 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

36. Functions of RH in 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

37. Wernicke - Lictheim’s House model of language

38. Wernicke-Geschwind model: Serial fashion for language processing. 7 components: Wernicke’s area Arcuate fasciculus Broca’s area Angular gyrus Primary auditory Cortex Primary visual cortex Primary motor cortex 

39. 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

40. Tripartite organization for language system 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

41. Dual Stream Model of 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

42. 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.

43. 4. Language Asymmetry and Genetics  

44. FOXP2 Forkhead box P2 (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 S ubstituted a histidine for an arginine at site 553 in the FOXP2 sequence

45. Inferior frontal Basal Ganglia loop Inferior frontal – cerebellum loop -- Nature R eviews Neuroscience (2005) 6; 131-138

46. Lateralization of gene expression 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

47. Large & diffused semantic fields Small & focused semantic fields Multiple distantly related words Coarse interpretation Summation of weak activation

48. Bicêtre Hospital, the place of Leborgne's illness. -- Credit: National Library of France.

49. We’ve come a long 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.