Is one (right) hemisphere enough? Neurolinguistic architecture in a case with very early left emispherectomy

In children with acquired left hemisphere lesion everyday linguistic skills may be largely preserved(1-3): the neural correlates underlying this preservation are not well known yet. We used fMRI to explore major aspects of neurolinguistic organization for single word processing in a 16 yrs old patient (EB) who received a left hemispherectomy at the age of 2.5 years for a haemorrhagic angio-cavernoma. EB was severely aphasic after surgery for at least one year. At the age of fMRI testing, EB’s linguistic skills were seemingly close to normal: however, when formally tested, he was lagging behind in lexical retrieval and comprehension. We assessed cerebral activations for the automatic/voluntary dissociation in word retrieval; we also contrasted these activations to those associated with auditory and visual word presentation. For each task we assessed whether the areas activated in EB were comparable to the left hemispheric ones activated in 24 right-handed controls. The fMRI experiments showed much similarity between the right hemispheric patterns in EB and the left hemispheric ones of the controls with the exception of a larger prefrontal recruitment for tasks with limited cognitive load (e.g. automatic series, auditory word listening). In addition, consistent with EB’s difficulty in lexical decision tasks when reading, we found reduced activation in the temporo-occipital region normally associated with reading and hypoactivated in developmental dyslexia(4). Taken together, these findings suggest that the lone right hemisphere of hemispherectomized patients may have a neuronal implementation of language similar to that of dominant left hemispheres even in their pathological manifestations, such as those of dyslexia. References 1. Woods, B.T., Teuber, H.L., 1978. Changing patterns of childhood aphasia. Ann Neurol 3, 273-280. 2. Cossu, G., Da Prati, E., Marshall, J.C., 1995. Deep dyslexia and the right hemisphere hypothesis: spoken and written language after extensive left hemisphere lesion in a 12-year-old boy. Cognitive neuropsychology 12, 391-407. 3. Vargha-Khadem, F., Carr, L.J., Isaacs, E., Brett, E., Adams, C., Mishkin, M., 1997. Onset of speech after left hemispherectomy in a nine-year-old boy. Brain 120 ( Pt 1), 159-182. 4. Paulesu, E., Demonet, J.F., Fazio, F., McCrory, E., Chanoine, V., Brunswick, N., Cappa, S.F., Cossu, G., Habib, M., Frith, C.D., Frith, U., 2001. Dyslexia: cultural diversity and biological unity. Science 291, 2165-2167.