Computed tomography scan is the most commonly used medical diagnostic procedure for head exploration in children. Repeated use of computed tomography scan can lead to a relative high cumulative dose. Long-term effects of brain exposure, at low to moderate doses (≤ 2 Gy) of ionizing radiation on cognitive functions, such as learning and memory processes, are not well established in humans and are a scientist issue of importance. Among brain structures potentially impacted by irradiation, hippocampus is a structure of interest because of its involvement in cognitive processes. In the hippocampus, new neurons are continuously generated in the subgranular zone of the dentate gyrus during postnatal and adult life. The adult-born neurons integrated in the dorsal dentate gyrus play an important role in several “hippocampal-dependent “forms of memory. The aim of our project is to study, in mouse model, the impact of postnatal irradiation on spatial learning and memory, and the processes of adult hippocampal neurogenesis. For that, two models of exposure were realized on ten-day-old mice: whole-brain exposure and targeted exposure of the dorsal dentate gyrus. Dose range of X-ray (0.25, 0.5, 1 and 2 Gy) is performed to study the complexity of dose response relationship at low to moderate doses. Spatial learning and memory abilities were assessed three months after exposure using a massed water-maze behavioral task. Our results demonstrated that spatial learning is not altered by irradiation in both models and for each dose. Long term spatial memory is impacted only after X-ray exposure of the dorsal dentate gyrus at 1Gy. Thus, nonlinear dose effects on memory processes after targeted irradiation were highlighted. By immunohistochemistry experiment, results bring out that the number of immature neurons is not impacted after exposure to 1Gy in both models. Mature neurons are significantly decreased in targeted model compare to whole-brain exposure. Conversely, glial and stem cells are significantly increased after targeted exposure compared to whole-brain exposure. A study of proliferation process is on going. This work will improve our understanding of how low to moderate doses of ionizing radiations could impact brain and bring scientific clues for the children radioprotection system.