Dissociation of Cognitive Changes under Unilateral Exposure of the Hippocampus to Radiation

Abstract: Although the key position of the hippocampus (HP) in memory processes is not in doubt, the specifics of its involvement in cognitive processes is 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 hippocampal neurogenesis. Hippocampal exposure to radiation, which inhibits the processes of neurogenesis, can serve as a model for studying this relationship. A homogeneous sample of 28 patients with parasellar meningiomas adjacent to the HP was studied. The mean age of participants was 51.18 years (SD = 10.16). Fifteen patients were diagnosed with a left-sided tumor (LST) and 13 patients with a right-sided tumor (RST). 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 inevitably received a dose comparable to the dose in the tumor. The study using the original technique for assessing visual memory was carried out before the start of RT, immediately after its completion, and 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, on more pronounced long-term cognitive consequences of ionizing effects on the left hemispheric HP.