First 'atlas' of human brain created 3D rendering showing the expression of a single gene across the cortex of two human brains, revealing areas with higher (red) and lower (green) expression. Credit: Allen Institute for Brain Science 19 (UPI) -- An atlas of the human brain showing activity of genes across the entire organ could shed light on neurological and psychiatric conditions, U.S. researchers say. Researchers at the Allen Institute for Brain Science in Seattle created the map from genetic analyses of about 900 specific parts of two "clinically unremarkable" brains secured from deceased donors. The atlas will provide a baseline to compare with the genetic activity of diseased brains and so reveal clues about factors that may underlie neurological and psychiatric conditions, researchers said. "The human brain is the most complex structure known to mankind and one of the greatest challenges in modern biology is to understand how it is built and organized," Seth Grant, a professor of molecular neuroscience at Edinburgh University who worked on the map told Britain's The Guardian newspaper. This allows us for the first time to overlay the human genome on to the human brain. It gives us essentially the Rosetta stone for understanding the link between the genome and the brain, and gives us a path forward to decoding how genetic disorders impact and produce brain disease," he said. The atlas, in which the genetic results are overlaid on to a 3D image of the brain, is freely available for researchers to use online, the Allen Institute said.