Language organisation in left perinatal stroke

Right-hemispheric organisation of language has been observed following early left-sided brain lesions. The role of the site of damage is still controversial, as other aspects influence the pattern of speech organisation including timing of the lesion and the presence of epilepsy. We studied a group of 10 term-born children homogeneous for timing/type of lesion and clinical picture. All subjects had left perinatal arterial stroke, right hemiplegia, normal cognitive functions and no or easily controlled epileptic seizures. In half the patients, the lesion clearly involved Broca's area, in the other half it was remote from it. Language lateralization was explored by an fMRI covert rhyme generation task. Eight of 10 subjects showed a right lateralisation of language, including all five patients with a damaged left Broca and 3/5 of those without it. Group analysis in patients with right hemispheric organisation showed brain activations homotopic to those found in the left hemisphere of a matched control group. Our findings confirm that, at the end of gestation, the human brain exhibits extraordinary (re-)organisational capabilities. Language organisation in the right hemisphere is favoured by the presence of destructive lesions of the left Broca's area at birth, and occurs in brain regions homotopic to those usually involved in language processing.