Kate Turner and Tom Hawkins, UCL.
Researchers studying the brain love zebrafish. Their embryos are clear, making them easy to observe, and their brains develop very quickly. What’s more, scientists have sequenced the entire zebrafish genome — by knowing which genes do what, scientists can tinker with the genetic blueprint to model a host of neurological conditions from depression to autism spectrum disorders. Not bad for such a small fish. In the above image of a four-day old zebrafish, scientists have highlighted neural tracts — bundles of axons that carry signals across the brain — in green. They’ve also isolated neruopil (magenta), a dense jungle of axon terminals and dendrites — the site of cellular connections and the place where individual cells form the circuits that define all brain activity.