Last year, neuroscientists unveiled a remarkable new technique called CLARITY that makes whole mouse brains invisible. And now, they're proving it's not just a cool trick. A striking new video shows the complex circuits that light up when mice experience fear or cocaine addiction.


Nature reports on a study led by Stanford neuroscientist Li Ye and Karl Deisseroth where they trained two sets of mice to associate a box with either a painful electric shock or a more pleasurable injection of cocaine. These mice were special: They had been genetically engineered so that their neurons express a fluorescent protein when active.

Once trained, the mice were put in the box and then killed, as they were experiencing either fear or anticipation. Their brains were then removed and bathed in a solution that replaces opaque fats in the brain tissue with a clear gel. The structure of the brain, as well as proteins, remain intact. With that, scientists can easily visualize the fluorescent proteins of the neurons that were active during fear and cocaine anticipation.


Peering inside brains as they work is the ultimate problem of neuroscience, and CLARITY is one major advance toward it. Bonus: It's also incredibly pretty. [Nature]