Le développement visuel et cognitif chez les enfants nés à terme ou prématurément

Over the past 25 years, researches about vision development in humans using cerebral electrophysiology and visual evoked potentials (VEPs) have helped to document several functions related to the visual cortex. However, the development of some of these features (e.g. texture segregation), or how it is affected by a preterm birth, are remaining aspects that need to be further explored. Moreover, given the importance of vision in the development of many cognitive functions (e.g. reading, visual-motor skills), more studies are becoming interested in the relation between vision and cognition. The general objectives of this thesis were to study vision development in children born full-term and born preterm using electrophysiology, and to document the impacts of preterm birth on visual and cognitive development. Two studies were realized.  The aim of the first study was to investigate the development of central visual pathways in children born preterm during the first year of life and at school-age, and to establish their cognitive and behavioral profile at school age. Using a semi-longitudinal study design, 10 children born preterm were assessed at six months and at 7-8 years old with visual evoked potentials (VEPs) at both time points and cognitive and behavioral tests at school-age. Their results were compared to those of 10 age-matched children born full-term. At six months’ corrected age, we found no significant differences between preterm and full-term groups for either amplitude or latency of N1 and P1 components. At school-age, the preterm group manifested significantly higher N1 amplitudes in the preferential P and the co-stimulating M-P conditions, and tended to show higher P1 amplitudes in the preferential M condition, in comparison to the full-term group. We found no significant differences in cognitive and behavioral measures at school-age. These results suggest that preterm birth impacts on visual pathways development.   The aim of the second study was to characterize the development of visual texture segregation processes during early childhood in children born full-term and children born preterm using VEPs and a cross-sectional study design. Forty-five full-term and 43 preterm children were tested at either 12, 24 or 36 months of age (corrected age for prematurity at 12 and 24 months old). Results show a significant N2 latency reduction between 12 and 36 months of age in response to orientation, texture, and texture segregation stimulus conditions and a significant N2 amplitude reduction for orientation between 12 and 24 months, as well as for texture between 12 and 24 months, and 12 and 36 months. Comparison between full-term and preterm children indicated significantly lower N2 amplitude for the preterm group at 12 months for orientation and texture. Although these differences were no longer apparent at 24 months of age, our results appear to reflect a maturational delay in preterm children in both lower-level and higher-level visual processing during, at least, early childhood.  In conclusion, our results indicate that preterm birth, even without significant neurological impairment, has an adverse effect on the development of visual functions at certain times during child development and therefore, highlight the importance to further investigate its medium and long term effects (ex. on cognition, behavior, or at school).

Keyphrases: Cognition, Preterm birth, Childhood, Visual development, Visual pathways, Higher-level visual processing, Electroencephalogram (EEG), Visual evoked potential (VEP), Behavior