Reductionist biology—examining individual brain parts, neural circuits and molecules—has brought us a long way, but it alone cannot explain the workings of the human brain, an information processor within our skull that is perhaps unparalleled anywhere in the universe. We must construct as well as reduce and build as well as dissect. To do that, we need a new paradigm that combines both analysis and synthesis. The father of reductionism, French philosopher René Descartes, wrote about the need to investigate the parts and then reassemble them to re-create the whole.