Hemispheric dominance for language: quantitative aspects

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Abstract
Data extracted from 29 reported series of cases were analyzed for the purpose of assessing the contribution of each hemisphere to the handling of language in left-handers (including ambidexters), impure right-handers (right-handers with personal or familial traits of left-handedness) and pure right-handers (right-handers without such traits). It was concluded that the representation of language in the two hemispheres varies over a continuous spectrum, from strict left-brainedness, through various degrees of ambilaterality (favoring one or the other hemisphere), to strict right-brainedness. Calculations based on the data led to estimates of (a) the percentage of subjects that will become aphasic following lesions of the left, the right or either hemisphere, and (b) the percentage of subjects that will be able to compensate, partially or completely, with the remaining hemisphere. All numerical results obtained were accounted for by a simple anatomical model based on estimates of (a) the frequency distribution of the subjects with regard to the percentage of a language area occupying each hemisphere, according to handedness, and (b) the percentage of a language area that must be destroyed so that aphasia will appear, and the percentage that must be spared so that partial improvement or total recovery will ensue.