Neurons in young brains form a riot of interconnections that fan out in all directions, with multiple nerve cells often converging on a single target cell. As brains mature, some of these overlapping connections are pruned. Being able to visualize this pruning process for individual cells could help scientists answer fundamental questions about how information is propagated through the neural network. Yet understanding how different connections are strengthened or eliminated has proved difficult, because neighboring neurons stained with a single dye blur together under a microscope.
But in 2007, a team led by Jeff Lichtman, a neurobiologist at Harvard University, developed a technique called Brainbow to label neurons in mouse brains with a palette of over 100 different colors, described in this month's Hot Paper. The key to the technique was creating transgenic mice with genes for the protein Cre recombinase (cre), as well as a custom-built snippet of DNA ...
