"The effect of spatial memory tasks on activation and survival of immature adult-born neurons"
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New neurons are continually added to distinct areas of the brain during adulthood. Although it is known that these adult-born neurons in the hippocampus are somehow implicated in learning, it is not known however, when or how the newborn cells participate in hippocampal functioning. When during maturation the newborn neurons have the potential of contributing to the functioning of the network, is a question which has yielded conflicting results. Researchers find that the newborn cells show increases in activity if the animal is exposed to an experience/environment that was encountered when the neurons were immature. However, the age the neurons need to be for the immature encounter to have an enhanced effect, varies with studies. For this reason, a part of the current project aims at establishing if this age- difference in activity might be due to aspects of the task or memory processing (encoding or retrieval). In other words, this part of the project asks if the age-associated participation might vary with type of processing conducted by the network. Approximately 50%, of adult-born neurons die within their first 4 weeks of age. The survival of immature neurons have been found to be affected by various factors, amongst them either memory processing or experience. The critical period of 1-2 weeks of age is used to test if two different tasks both relying on the hippocampus, might affect long-term survival differently. Immature neurons in different species have been shown to express maturity markers and neuronal activity marker in a different degree, suggesting that maturation might occur on separate timelines between species. The potential conclusion from these findings is that the newborn neurons in rats mature earlier than in mice. The present project investigated if this truly is the case by evaluating natural occurring activity. In other words, if the newborn cells during immaturity can be affected by experience/memory processing specifically compared to controls. The present projects show that firstly: If indeed encoding and retrieval was used to complete the tasks, the difference in activity found in the earlier studies is concluded to not be due to these types of processing. Secondly: that survival is affected differently depending on what type of task/experience is conducted. Thirdly: that neuronal activity following experience in the present project cannot be ascribed directly to the memory processing conducted by the network hours before.