A team at Stanford University has made brains transparent, allowing entire networks of neurons to be highlighted and then viewed through an optical microscope. In the past, it has only been possible to image slices of organs such as the brain. First, Karl Deisseroth and his colleagues propped up the cells in a whole mouse brain using a scaffold of fibrogel, before removing all the fat surrounding the cells. The technique – details of which are published in the latest issue of Nature – also works on human brains, potentially revealing how changes to the connectivity of neurons cause conditions such as autism