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Language Lateralization and Psychosis
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Book description

In 1861 Paul Broca discovered that, in most individuals, the left hemisphere of the brain is dominant for language. Taking language as an example, the first part of this book explains the normal development of bodily asymmetry and lateralization, its association with hand preference, genetic aspects, geographical differences and the influence of gender. The coverage then moves on to review the association between language lateralization and psychosis, describing findings in patients with schizophrenia to suggest the dominant hemisphere may fail to completely inhibit the language areas in the non-dominant half. The language allowed to 'release' from the right hemisphere can lead to psychotic symptoms including auditory verbal hallucinations and formal thought disorder. This book should be read by psychiatrists, neurologists and neuroscientists working in the field of psychosis and other brain scientists interested in laterality.


'… intriguing and interesting … a welcome addition to the field. … a fascinating theory … an excellent and absorbing new book on the importance of cerebral laterality to psychotic disorders. Anyone wanting to understand more about how psychosis and the functional organization of the brain interact should read this valuable book.'

Source: Doody's Notes

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  • 8 - Hand-preference and population schizotypy:
    pp 121-132
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    The field of left-right (LR) asymmetry is currently at an exciting point, with considerable body of genetic and cell-biological data elucidating dozens of mechanisms in a range of vertebrate and invertebrate model species. The patterning of the LR axis can conceptually be broken down into several distinct steps that have served as a working model for the field. The embryo orients the LR axis with respect to the dorsal-ventral and the anterior-posterior axes, hence being able to "tell its left from its right". Next, the embryo must set up a stable biophysical or molecular difference between the left and right sides, which can be imposed upon multicellular fields as the embryo divides. Third, cell fields on the left and right sides execute transcriptional cascades that set up differential gene expression patterns impinging on organ primordia. Fourth, the various organs make use of this asymmetric information as they undergo asymmetric morphogenesis.
  • 9 - Functional imaging studies on language lateralization in schizophrenia patients
    pp 133-146
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    This chapter provides an overview of animal asymmetries of handedness, spatial orientation, and communication. For all three systems, the chapter provides a detailed knowledge on the behavioral and neural asymmetries in humans. It captures the details into a wider framework of cerebral asymmetries in animals, including humans. The chapter reviews the handedness studies with diverse animal species that make functional asymmetries for spatial cognition likely. It also reviews the spatial orientation studies, which shows that the hemispheres of mammals and birds contribute differentially to spatial cognition, although both sides are to some degree able to utilize the strategy of the other. The experiments with bird species show that spatial navigation requires different computational strategies of the left and the right brain. Experiments on asymmetries in the perception and production of communicatory signals cover a wide range of species from chimpanzees to frogs.
  • 10 - The role of the right hemisphere for language in schizophrenia
    pp 147-156
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    This chapter presents an overview of the various sets of data that provide insight into human handedness history and geography. The history of handedness before 1800 consists almost entirely of a few isolated points, which often are illuminated only briefly through indirect evidence that has to be treated with great care. Data on handedness from the prehistoric period and pre-literate societies are necessarily indirect, take many forms, and can be difficult to interpret. A classic epidemiological method for distinguishing the effects of genes and culture is to observe migrants between two countries which differ in some characteristic. The chapter provides a clear demonstration that rates of left-handedness vary between different countries. Most explanations in biology distinguish nature and nurture, which to a large extent can be conceptualized as genes and environment. Social pressure can take many forms, and it is useful to distinguish between direct and indirect social pressure.
  • 11 - Auditory verbal hallucinations and language lateralization
    pp 157-168
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    This chapter summarizes literature on handedness, language, and cerebral asymmetry as evidenced by lesion and neuroimaging studies. The development of non-invasive techniques has allowed us to determine functional brain asymmetries even in healthy subjects. The chapter comments on the possible origin of dexterity and language lateralization, the individual differences in laterality, as well as the distribution of laterality at the population level. Human brain imaging studies indicate that Broca's area, which is located in the pars opercularis of the inferior frontal gyrus, may be part of the human mirror neuron system as well as the superior temporal sulcus and the inferior parietal lobule. The relation between handedness and language lateralization invites speculation on the underlying neural causes. Lateralization of language functions should aid the processing demands required for a full exhaustion of linguistic capacities.
  • 12 - Language lateralization in patients with formal thought disorder
    pp 169-180
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    Modern theories of genetic influence on lateralization suggest that random or fluctuating asymmetry has an important role. Theories of directional asymmetry or chance can be distinguished from the right shift (RS) theory that accidental asymmetries are universal for bilaterally symmetrical organisms. The right shift (RS) theory developed through a series of stages of empirical research and theoretical analysis. Briefly, the theory suggests that degrees of hand preference map onto a non-genetic normal distribution of asymmetry for hand skill, a continuum of right minus left (R - L) skill. The RS model explains relations between handedness and cerebral speech laterality. The key argument, for most skeptics of genetic influence on handedness, is the discordance of monozygotic (MZ) pairs. An early attempt to study the inheritance of brain asymmetries used a dichotic listening test in 49 families.
  • 13 - LRRTM1:
    pp 181-196
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    This chapter discusses several twin-specific factors that could affect handedness in twins and thereby decrease concordance rates in twins. The classical method to determine the genetic contribution to a trait is to compare concordance for that trait between monozygotic (identical) and dizygotic (fraternal) twins. The chapter also discusses which implications the model of inheritance for handedness has on concordance rates in twins. It investigates the effect of special twin factors, such as perinatal trauma and mirror-imaging on concordance rates in twins. Understanding the role of these factors in twins will help to interpret the results of twins studies and may resolve part of the controversy about genetic aspects of handedness and language lateralization. An explanation for the low concordance for handedness and lateralization in twin pairs could be the presence of a non-genetic factor that affects twins more than singletons.


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