Although the key position of the hippocampus (HP) in memory processes is not in doubt, the specifics of its participation in cognitive processes are far from being established. At the same time, the role of the HP in differentiating the novelty of impressions is often discussed in the context of adult HP neurogenesis. Radiation exposure to the HP, which inhibits the processes of neurogenesis, can serve as a model for studying this relationship. A homogeneous sample of 28 patients with meningiomas of the chiasmal-sellar area adjacent to the HP was studied. 15 patients were diagnosed with a left-sided location of the tumor and 13 patients with a right-sided one. The two groups were comparable in terms of demographic, clinical and morphometric characteristics. In order to stop the growth of the tumor, the patients underwent radiation therapy (RT), in which the HP on the side of the pathological process was forced to receive a dose comparable to the dose in the tumor. The study using the original technique was carried out before the start of RT, immediately after its completion, 6 and 12 months after the end of RT. Data were obtained on earlier changes in memory characteristics mediated by the right hippocampal region, but at the same time — more pronounced long-term cognitive consequences of ionizing effects on the HP of the left hemisphere.