Neuropsychologie, plasticité et épilepsie infantile

Abstract

Depuis 1979, à l’hôpital Sainte-Justine de Montréal, notre équipe étudie les effets de l’épilepsie sur le développement psycho-moteur et cognitif de l’enfant. Nous avons d’abord exploré l’étendue et tenté de définir les limites de la plasticité cérébrale d’enfants ayant subi une neurochirurgie précoce (callosotomie, hémisphérectomie). Nous avons démontré que les enfants ayant été opérés avant la puberté bénéficient encore de cette plasticité. En revanche, les mécanismes de compensation sont modestes pour ce qui touche les informations dont la complexité exige d’être traitée par ces structures cérébrales. Par la suite, nous avons étudié les répercussions neuropsychologiques des épilepsies focales, particulièrement les épilepsies frontales et temporales. Les résultats ont révélé que les enfants présentent les mêmes déficits localisés que les adultes, infirmant donc l’idée selon laquelle l’épilepsie infantile entraîne des effets indifférenciés. Depuis peu, nous profitons des techniques d’imagerie fonctionnelle (électrophysiologie de haute densité, magnétoencéphalographie, imagerie optique) pour explorer la propagation des effets de l’épilepsie sur la maturation cérébrale.

Epilepsy is one of the most frequent childhood disorders. While most cases are well controlled, approximately 30-50% are resistant to medical treatment. In these cases, neurosurgery may be an option. Since 1979, our team at the Sainte-Justine Hospital in Montreal has studied the impact of epilepsy on the psycho-motor and cognitive development of the affected children. The aim of a first series of studies was to explore the extent and limits of cerebral plasticity by investigating the neuropsychological sequelae of early versus late callosotomy and hemispherectomy. In keeping with the plasticity hypothesis, the results revealed that the children who were operated before puberty showed fewer deficits than those operated during adolescence or adulthood. However, the compensatory mechanisms available to them appeared to be limited with respect to the nature and complexity of the information they can process. For instance, young children having undergone section of the corpus callosum resembled individuals born without a corpus callosum (callosal agenesis) in that there did not show the typical disconnection deficits seen in adult “split-brain” patients. However, they exhibited deficits on tasks requiring interhemispheric integration of motor and visuo-motor information. By the same token, hemispherectomy patients were still able to make visual judgements in their “blind” visual field but they were found to be impaired on a variety of visual and auditory tasks (localization of a sound sources in space) requiring the participation of both hemispheres. In a second series of studies, carried out in collaboration with a Parisian team, we intended to describe the neuropsychological profile of focal epilepsies, specifically frontal and temporal epilepsy. Contrary to the common belief that childhood epilepsy would result in diffuse impairments, we were able to demonstrate that children manifest the same localized deficits as adult patients. In studies presently underway in our laboratories, we make use of functional neuroimaging techniques such as high density electrophysiology, optical imaging and magnetoencephalography to investigate pre-and postoperative language and memory functions and to study the impact of epilepsy on brain maturation.