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Paul Greengard was born on December 11, 1925. He was an American neuroscientist who shared the 2000 Nobel Prize in Physiology or Medicine with Arvid Carlsson and Eric Kandel for their discoveries concerning signal transduction in the nervous system. Greengard's research focused on the role of protein phosphorylation in synaptic plasticity, the ability of synapses to strengthen or weaken over time.