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Adult brain neurogenesis occurs in two regions that surround blood vessels in the subventricular zone and in the dentate gyrus of the hippocampus, but little has been known about whether blood-borne factors affect neurogenesis.
To investigate this issue, researchers connected the blood systems of old and young adult mice (parabiosis) and compared neurogenesis, fear learning, and memory in parabiotic young–young, old–old, and young–old mice. In young–old mice, after parabiotic connections, neurogenesis in the brains of young mice began to resemble that of old mice, and the brains of the old mice more resembled younger ones. Changes in the learning tasks were similar to the anatomical changes. Brains and learning in young–young and old–old par…