Hemispheric Lateralisation

10 Key excerpts on "Hemispheric Lateralisation"

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  The Mind-Brain Relationship

  • Regina Pally(Author)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  In this century, in the 1930s, Lange revitalised interest in the central importance of the right hemisphere. He recognised that the right hemisphere provides a general contextual background to a person’s world view. During the 1960s the initial work of Sperry and Gazzaniga (Gazzaniga et al., 1962) at first seemed to corroborate the ‘two minds, two consciousnesses’ view held by some late nineteenth-century scientists. Subsequent work, however, resulted in the now generally accepted ‘asymmetric but integrated’ perspective. The right and left cerebral cortex are each lateralised for specialised functions, but in the healthy brain the two hemispheres share their information and operate collaboratively (Joseph, 1996; Deacon, 1997; Gazzaniga, 1995; Ornstein, 1997).

  Research regarding latéralisation of specialised functions pertains mostly to cortical functions. However, it must be remembered that specialised functions of each cortex are influenced by input from subcortical structures as well as from other cortical sites in the same or opposite hemisphere. According to Deacon, functional asymmetry evolved because in certain circumstances organisms must prioritise, and have only one goal, express only one action, or speak only one thought. For these particular functions only one hemisphere must have the advantage.

  Neuroscientists assume that the reason that language and fine motor movements are lateralised to the left cerebral cortex and emotion and musical ability to the right cerebral cortex is a fundamental difference between the left and right cortices with respect to information processing (Galin, 1974; Tucker, 1981). The left is better at analysing rapid temporal-sequential aspects of information. Therefore the left hemisphere more readily identifies ‘details’ and notices precise distinctions, rendering an advantage to the left in the specialised functions of language, causal relationships and fine motor movements. By contrast, the right is better at analysing the global, overall relationship aspects of information. Therefore the right more readily identifies context and gets the overall picture of the situation, giving an advantage to the right hemisphere in processing social interactions, emotional experience and visual-spatial tasks. One metaphor often used is that the left is a digital ‘computer’ and the right an analogue ‘computer. Another is that the left provides the ‘text’ and the right the ‘context’.

  Hemispheric dominance is relative, not absolute. Ornstein (1997) compares this to the ‘winner takes all’ in politics, where a 51 per cent majority can win the election. Translated into neuroscience this means a hemisphere does not function 100 per cent in its area of speciality, only relatively

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  Autism Imaging and Devices

  • Manuel F. Casanova, Ayman El-Baz, Jasjit S. Suri, Manuel F. Casanova, Ayman El-Baz, Jasjit S. Suri(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Instead, lateralization indicates that one side of the brain plays a greater role in a given cognitive process than the other, that is, their involvement is asymmetric. 137 Atypical hemispheric asymmetries in autism spectrum disorders 81 Language Language is the paradigmatic lateralized function. Though the idea that different regions of the brain are specialized for different types of function is now taken for granted, this knowledge is comparatively new. French neurosurgeon Paul Broca (1865) first suggested that the brain is lateralized for articulate language, based on his observation of patients with speech impairments. At autopsy, he noticed a pattern: patients who presented with speech problems had damage to the left hemisphere. In the 150 years since Broca’s discovery, confirmatory research has grown, indicating that though both sides of the brain contribute to language pro- cessing (see Lindell 2006), the left hemisphere is undoubtedly the supe- rior language processor in the typical brain. As left hemisphere lateralization is typically associated with normal language function, it follows that atypical language lateralization may compromise language ability. And indeed, people with developmental disorders that impair language function, including dyslexia (Xu et al. 2015), ADHD (Hale et al. 2005), and specific language impairment (Hodge et al. 2010), show evidence of reduced and/or reversed left hemi- sphere lateralization for language. Language and communication impairments form a core diagnostic criterion in ASD, and additionally play a key prognostic role (Herbert et al. 2002). For example, in children with ASD, the early presence of speech (before age 5, Mody and Belliveau 2012; before age 2, Mayo et al. 2013) is considered the strongest predictor of favorable outcomes.

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  Cortical Functions

  • John Stirling(Author)
  • 2020(Publication Date)
  • Routledge

    (Publisher)

  4

  Lateralisation

  Introduction Structural differences The split brain syndrome Callosal agenesis Asymmetries in normal individuals What is lateralised? Inter-hemispheric transfer via the corpus callosum Individual differences in brain organisation Summary

  Introduction

  As I mentioned in Chapter 2 , at first glance, the two cortical hemispheres look pretty much like mirror images of each other. Yet closer inspection reveals many subtle differences in structure. Behavioural studies suggest differences in function too. The study of lateralisation is the study of the distinct patterns of psychological functioning seen in the two hemispheres. Hemispheric specialisation is also sometimes known as asymmetry of function because of the different (asymmetric) responsibilities that psychologists have observed. In this chapter, we consider the various ways that scientists have examined this asymmetry, and the conclusions that they have drawn from their research.

  Structural differences

  The two hemispheres of the adult human brain are not mirror images of one another, and differ in a number of characteristic ways.

  •  Viewed from the top of the head, the right frontal lobe extends further forward, and the left occipital lobe further back. •  The dividing line between the frontal and temporal lobes (known as the Sylvian fissure) is longer and less sloped on the left side than the right. •  A region of temporal lobe adjacent to the Sylvian fissure is much larger on the left than the right. This area of cortex has been linked to language comprehension for at least 100 years.

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  Hemispheric Communication

  Mechanisms and Models

  • Frederick L. Kitterle(Author)
  • 2020(Publication Date)
  • Routledge

    (Publisher)

  2 Neuroanatomical Bases of Hemispheric Functional Specialization in the Human Brain: Possible Developmental Factors 1 Sandra F. Witelson McMaster University

  Functional Asymmetry: Nature and Ontogeny

  Hemispheric functional specialization or functional asymmetry is a well-established characteristic of functional organization in the human brain. In essence, the right and left hemispheres have different roles in mediating various behaviors and higher mental processes. Tasks involving speech production, phonemic discrimination; comprehension of oral and written language; the ability to write; performance of voluntary finger, limb, and oral movements; and the perception of sequences of stimuli are more dependent on left- than right-hemisphere functioning in most people. In contrast, tasks involving the perception of two- and three-dimensional visual or tactual shapes, spatial position and orientation of stimuli, the perception of faces and colors, mental rotation of three-dimensional shapes, the ability to direct attention to both lateral sensory fields, the perception of musical chords and melodies, aspects of the perception of emotional stimuli and prosodie features of speech, and the abilities to dress oneself and to construct block models are more dependent on the right hemisphere. In the past decade, numerous books have summarized these findings based on the study of brain-damaged people with unilateral lesions, people who have undergone commissurotomy, and neurologically intact people who were tested with various behavioral and perceptual tests involving right- and left-sided input or output (e.g., Beaton, 1985; Boller & Grafman, 1988-1990; Bradshaw & Nettleton, 1983; Bryden, 1982; Corballis, 1983; H. Damasio & A. Damasio, 1990; Geschwind & Galaburda, 1984; Hannay, 1986; Heilman & Valenstein, 1985; Heilige, 1983; Kolb & Whishaw, 1990; Molfese & Segalowitz, 1988; Ottoson, 1987).

  However, several key issues related to hemispheric specialization remain unresolved. First, the lists of tests that are more dependent on one hemisphere or the other are continually expanding. There is no demonstration, however, of what specific cognitive functions are common to each set of skills and are indicative of the type or types of processing that each hemisphere is specialized for. The numerous dimensions postulated for hemispheric differences, such as verbal versus nonverbal or analytic versus synthetic, are merely inferred hypotheses derived from the numerous tasks studied, of what the essential functional characteristics of the hemispheres are. Moreover, it has been shown that it is not only the nature of the task stimuli, but also the strategy or process the subject uses to perform the task, that determines which hemisphere is dominant in processing for that task. Currently, a widely used working hypothesis is that the left hemisphere is specialized for analytic, sequential, time-dependent functions, and the right hemisphere is specialized for synthetic, spatial perceptual functions (e.g., Bradshaw & Nettleton, 1983).

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  Principles Of Biopsychology

  • Simon Greene(Author)
  • 2013(Publication Date)
  • Psychology Press

    (Publisher)

  Some authors have suggested that people may be characterised by their “dominant” hemisphere; left hemisphere people are analytical, verbal, rational, scientific, whereas their right hemisphere counterparts are creative, intuitive, visuo-spatial, artistic, emotional. However, it is only in the artificial conditions of the laboratory that we can even try to separate out hemisphere functions. Any human endeavour is bound to contain elements of both “styles”. Einstein was a scientist, but the theory of relativity was also a creative enterprise—the original ideas did not emerge fully formed. Leonardo da Vinci was perhaps as great an artist and inventor as has ever lived, but all his work shows tremendous attention to detail. Even for us lesser mortals virtually everything we do represents contributions from both hemispheres; that is inevitable given that we have a corpus callosum to ensure that the activities of the two sides of the brain are synchronised and integrated. Despite the attraction of seeing the hemispheres in general terms, as either analytic or visuo-spatial, most people would accept that the left hemisphere does contain specific mechanisms for language. Of all the tests of hemisphere lateralisation, the most reliable is the Wada test for speech laterality. This technique uses the fact, mentioned earlier, that each hemisphere has a separate blood supply. An anaesthetic (e.g. sodium barbital) is injected into the carotid artery supplying one hemisphere. The patient is asked to read aloud. If the anaesthetised hemisphere contains the language system, then speech will temporarily fade away; the test is used to check on speech laterality before brain surgery. The Wada test shows that over 95% of right-handed subjects have speech in the left hemisphere. Note that this is a test of reading comprehension and speech production together. Tests of language comprehension alone (i.e

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  The Lateralized Brain

  The Neuroscience and Evolution of Hemispheric Asymmetries

  • Sebastian Ocklenburg, Onur Güntürkün, Onur Gunturkun(Authors)
  • 2017(Publication Date)
  • Academic Press

    (Publisher)

  While both research in split-brain patients and the results from the Wada test indicate that speech processing is impossible without the left hemisphere in most individuals, the notion that one hemisphere completely controls a complex cognitive function such as language processing is grossly oversimplified. Language processing is not one unified brain function, but consists of several functional modules, each showing its own typical pattern of hemispheric asymmetries. For example, when we communicate with another human being, we participate in both speech perception—such as hearing and understanding the words—and speech production—such as choosing and speaking the words. In addition to spoken speech, language processing can also refer to written material—such as in reading or writing a sentence. Moreover, there are also non-verbal aspects of language—such as gesturing or facial movements—and some languages—such as sign language—that are based completely on non-verbal means of communication.

  Motor Aspects of Language Lateralization

  Human language is the most complex system of communication any species on earth has ever developed. While many species use vocal calls to communicate, only humans have developed articulate speech that goes beyond cries of warning, distress, or courtship behavior. One of the major theories regarding the evolution of human language is the hypothesis that it evolved from ancient gestural systems of communication, with vocalizations being gradually incorporated.6 This implies that left-hemispheric language lateralization might already be evident on the level of motor gestures carried out, e.g., with the arms or the face. Indeed, it was shown that people gesture more with their right hand than with their left during speaking, while no differences between the hands were observed for silent activities.

  7 ,8

  Other motor aspects of language are also lateralized. During speech, the right side of the mouth opens faster and reaches higher maximal opening values in most individuals, with about 76% showing a greater right-side opening

  9 ,10

  (Fig. 4.2

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  Functions of the Right Cerebral Hemisphere

  • Andrew Young(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  It must be admitted that, while the evidence accumulates in favour of hemisphere specialisation, the use of almost any method must be regarded with some caution. While increasingly unlikely, it is still possible that alternative explanations not so directly based upon cerebral anatomy may yet be found for many of the performance asymmetries thought to indicate hemisphere specialisation. It would be absurd to discount all the research evidence, often of considerable quality, which has been gathered, but it is not unreasonable to counsel continuing caution in its interpretation. The confusion which has come to be typical of this literature has at last created a mood of reappraisal and re-evaluation, and the result may well be an extensive re-assessment of the part played by cerebral specialisation in observed performance asymmetries. Finally, it is important not to lose sight of the inferential and correlational nature of most of the research methods which have been discussed above, and not to neglect the important fact that most neuropsychologists are not measuring the brain, but measuring human performance, and hoping that it tells them something about the brain. The degree to which it can is highly dependent upon the quality of both the theories and concepts expressed and the methodology 5 METHODS FOR STUDYING HEMISPHERIC FUNCTION 135 employed. Neuropsychologists neglect careful consideration of either at their peril. References A HERN , G. L. and S CHWARTZ , G. E. (1979). Differential latιralisation for positive versus negative emotion. Neuropsychologia 17, 693-698. A NDREWS , G. and Q UINN , P. T. (1972). Stuttering and cerebral dominance. Journal of Communication Disorders 5, 212. ANNETT, M . (1982). Handedness. In Divided Visual Field Studies of Cerebral Organisation (J. G. Beaumont, ed.), pp. 195-215. Academic Press, London and New York. BEAUMONT, J.

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  The Divided Therapist

  Hemispheric Difference and Contemporary Psychotherapy

  • Rod Tweedy(Author)
  • 2020(Publication Date)
  • Routledge

    (Publisher)

  The most popular assumption proposed that brain hemispheres deal with different types of information: the left hemisphere processes special signs like those present in natural and artificial languages, while the right hemisphere processes the natural nonverbal information such as images, melodies, and intonations of voice, and is responsible for orientation in space and within the subject’s own body. This concept seemed to be confirmed by the outcomes of the organic damages of left and right brain hemispheres. For instance, damage to the left temporal lobe is accompanied by motor and sensory aphasia while damage to the right parietal lobe is associated with disorientation in space. However, further investigations have shown that both hemispheres are able to deal with any kind of information (see Rotenberg, 1993). More reasonable is the concept of Gordon (1978) and Zaidel (1984), according to which the main function of the left hemisphere is the consequential analysis of any information, verbal as well as nonverbal, while the function of the right hemisphere is the simultaneous “grasping” of all elements of information in a holistic way. Such formation of the holistic image determines the comprehension of the object or event just before its consequential analysis. However, what is really grasped in a holistic way by the right hemisphere? The answer to this question requires the consideration of some philosophical aspects. The objective world that we deal with in our everyday life contains not only objects, subjects, and events. More important are the numerous interrelationships between these objects, subjects and events, both real and potential. It is precisely these interrelationships that make the objective world so vivid, rich, and dynamic. These interrelationships may be cooperative, complimentary, or contradictive. The left and right hemispheres differ according to the way they process these interrelationships

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  The Master and His Emissary

  The Divided Brain and the Making of the Western World

  • Iain McGilchrist(Author)
  • 2019(Publication Date)
  • (Publisher)

  11 The ratio of grey to white matter also differs. 12 The finding that there is more white matter in the right hemisphere, facilitating transfer across regions, also reflects its attention to the global picture, where the left hemisphere prioritises local communication, transfer of information within regions. Neurochemically the hemispheres differ in their sensitivity to hormones (for example, the right hemisphere is more sensitive to testosterone), 13 and to pharma-cological agents; 14 and they depend on preponderantly different neurotransmit-ters (the left hemisphere is more reliant on dopamine and the right hemisphere on noradrenaline). 15 Such structural and functional differences 16 at the brain level suggest there may indeed be basic differences in what the two hemispheres do . So what does the neuropsychological literature tell us about that? While it is true that we know a lot about what different, in some cases fairly minutely discriminated, areas within each hemisphere ‘do’, in the sense that we can answer the question ‘what’ it is that they appear to help mediate, we have tended to pay less attention to the ‘how’, the way in which they do this – not in the sense of the mechanism by which they do it, of which we have a rapidly increasing understanding, but in the sense of what aspect of a certain ‘function’ is being addressed. As soon as one starts to look in this way at the question – for example, not where language is, but what aspects of language are where – striking differ-ences between the hemispheres emerge. 17 THE PATHWAYS TO KNOWLEDGE Brain structure is easy to measure, function more problematic. So let me start by saying something of the ways in which we come to have knowledge of brain func-tioning, and some of the problems associated with them.

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  Language Functions and Brain Organization

  • S. J. Segalowitz(Author)
  • 2014(Publication Date)
  • Academic Press

    (Publisher)

  In order that effects due to task-related processing de-mands not be associated with bilingualism per se, it is necessary that uni- BILINGUALISM AND BRAIN LATERALIZATION 333 lingual and/or bilingual controls be routinely tested under identical experi-mental conditions. Taken together, findings from neuropsychological studies of bilinguals suggest that what distinguishes bilinguals from unilinguals, and particular bilingual subgroups from others, when differences do occur, is their use of strategies that deploy the specialized processes of the two hemispheres differently. As Gene see (1980) has noted, the functional competencies of the two hemispheres of early and late bilinguals may be no different from one another, nor from those of unilinguals. Rather, it may be the extent to which late bilinguals tend to use RH-based strategies in language pro-cessing that differs. Further theorizing on cerebral lateralization of language in bilinguals will, ultimately, have to address the issue of just what it is about bilingua-lism that may give rise to observed differences in processing strategy. To this end, psycholinguistic and cognitive research on bilingualism should provide some needed insights. ACKNOWLEDGMENTS I would like to thank Fred Genesee, Loraine Obier, E. Schneiderman, Sid Segalowitz, and Carlos Soares for providing useful comments on earlier drafts of this chapter. REFERENCES Albert, M., and Obier, L. (1978). The bilingual brain. New York: Academic Press. Anastosopoulos, G. (1959). Linksseitige Hémiplégie mit Alexie, Agraphie und Aphasie bei einem polyglotten Rechtshänder. Deutsche Zeitschrift für Nervenheilkunde, 179, 120— 144. Andrews, R. (1977). Aspects of language lateralization correlated with familial handedness. Neuropsychologia, 15, 769-778. * April, R. S., and Han, N. (1980a). Crossed aphasia in a right-handed bilingual Chinese man: A second case. Archives of Neurology, 6, 342-346. April, R. S., and Han, M.

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