Higher density of mental capacities in the left cerebral hemisphere of man: a quantitative investigation in children with localized cerebral lesions.

51 children with localized cerebral lesions were investigated with the British Ability Scales, Wechsler test, Porteus Mazes, Conners Teacher Rating Scale, and computerized tomography. The extent of the lesions was quantitatively determined. The IQ was 10 points lower in the left hemispheric lesions, although the right hemispheric lesions were larger. When corrected for size of lesions, the IQ is 17 points higher (p less than 0.05) in children with right than with left hemispheric early lesions. The children with left hemispheric lesions had also significantly more behavioural problems (Conners Scale). Children with bilateral lesions had 15 points lower IQ than those with unilateral lesions, although from the slightly larger extent one could expect only 3 points difference. There was no influence of hemiparesis or of epilepsy of the IQ independent of the extent of lesion. There was more plasticity of the hemisphere than of the lobes as shown by Wisconsin Card Sorting data. The higher density of mental capacities in the left cerebral hemisphere of man is explained by more efficient programs, and more dense packing of functions due to more training of the left cerebral hemisphere.