The Allen Institute team used a special technique to simultaneously capture a brain cell's 3-D shape, its unique electrical properties, and the suite of genes it switches on, from hundreds of individual neurons from the part of the mouse brain that processes visual information. But detailed visual descriptions of these cells have failed to reveal many insights about how different neurons carry out different jobs, let alone how individual cells might change in disease. Does the animal have fur or feathers? A beak, talons, hooves? The same is true for early studies of the brain-over the past 100 years, neuroscientists have realized that our neurons and other brain cells come in a wide variety of shapes and sizes. This tree describes not the millions of species that inhabit our planet, but the millions of neurons that make up the kumquat-sized brain of the lab mouse.īefore the advent of DNA sequencing, scientists used visual cues to define species. Just as biologists sketch evolutionary trees whose branches represent the development of different species and the relationships between them, some scientists now look to cells to draw another kind of family tree.