Beyond the initial discovery, Karl and his lab put an extraordinary amount of effort into making the technique accessible and available for neuroscientists around the world. The impact on the field here is in the distillation, in ensuring it could be applied to manifold questions and disease models. Richly deserved.

I participated in early work in optogenetics in larger brains, and Karl was my postdoc adviser. He is a deeply thoughtful and generous scientist. His book Projections unpacks some of his thinking as to how these tools may unravel and treat a panel of psychiatric conditions.