Thesis: The effects of cerebral exposure at low-to-moderate doses of ionizing radiation (IRs) on the adult cognition exposed during childhood are not clearly established in humans and there is a lack of experimental data on this subject. However, high-dose studies teach us that hippocampus (HPC) irradiation (IR), a site of adult neurogenesis, appears to participate in the development of cognitive impairment in adulthood. In this thesis, we investigated and compared the effects of postnatal whole brain (WB) or dorsal dentate gyrus (DDG) of HPC exposure , on long-term spatial memory (MSLT). Both models were exposed with a single dose of 0.25, 0.5, 1 or 2 Gy. Our results provide evidence that learning is not affected, 3 months after IR, in all our experimental conditions. The restitution of spatial memory, tested 10 days later, is altered only by DDG exposure at the dose of 1 Gy. Thus, we demonstrated that the dose-response relationship is not linear after localized exposure of GDD. We also demonstrated that WB or DDG exposure at the dose of 1 Gy has a different impact on adult hippocampal neurogenesis, a cellular process involved in MSLT. DDG exposure induces, among other things, an increase of cell proliferation while WB exposure induces their decrease, 2 months after IR. Only DDG exposure results in reducing the percentage of new mature neurons, 3 months after IR. The different alterations on adult hippocampal neurogenesis process could explain, in part, the results obtained during the restoration of spatial memory, in our two models exposed at 1 Gy. These results demonstrate that WB exposure is less deleterious than DDG exposure under our experimental conditions. This study helps improve our knowledge of the effects of exposure at low-to-moderate doses of IRs on the brain and a substructure of the hippocampus.