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Schizophrenia as failure of hemispheric dominance for language
Inhis Viewpoint article, Crow stated that the prevalence, incidence and clinical features of schizophrenia are remarkably similar across cultures1. However, there is evidence that schizophrenic symptomatology is markedly different between countries, and that, in some, the incidence of the disorder has increased by as much as 45% in a short period of time2. Crow indicated that a deficit inlateralization, particularly of the neural control of language, causes the illness1; this is in contrast with the suggestion that there are multiple and distributed neural controls of schizophrenic symptomatology3. In addition, Crow suggested that a ‘genetic factor’ controls the development of schizophrenia and therefore, on his hypothesis, language1. This contrasts with the suggestion that there areredundant genetic controls of the brain mechanisms of language4 and of the liability to schizophrenia5. If all of this is correct, we must conclude that schizophrenia has redundant external, neural and genetic controls. There are probably many, but let us conservatively assume there are four of each. This would allow for 4! x 4! x 4! = 13 824 combinations between genes, brain functions andschizophrenic symptoms. Does not this make the search for a neurobiology of schizophrenia an impossible project? Per Södersten Fredrik Sederholm
Karolinska Institute, Dept of Clinical Neuroscience, S-141 57 Huddinge, Sweden. References
1 Crow, T.J. (1997) Trends Neurosci. 20, 339–343 2 Kleinman, A. and Cohen, A. (1997) Sci. Am. 276, 74–77 3 Andreasen, N.C. (1997) Science 275, 1586–1593 4 Thomas, J.H.(1993) Trends Genet. 9, 395–399 5 Kirv, G. and Murray, R. (1997) Mol. Med. Today 3, 124–130
TO THE EDITOR
I am unhappy about Crow’s claims that: (1) lateralization of the human brain is its most specific feature; (2) all our heteromodal association areas have evolved via language lateralization; (3) language is what separates us from early hominids; (4) hemispheric specialization is howlanguage has evolved; and (5) language, not intelligence, is what has been selected for in our evolution. Laterality is pervasive throughout the animal kingdom1,2; although associated with language, it might not be an essential component, and many other factors, including Machiavellian intelligence3, might have been important for selection. Not all stutterers, developmental dysphasics or dyslexics are...
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