Karl Deisseroth was awarded the 2017 quadrennial 4 million euro Else Kröner Fresenius Prize today for the “discoveries of optogenetics and of hydrogel‐tissue chemistry, and for developing circuit‐level insight into depression”. In this opinion, he was invited to discuss the impact of optogenetics and hydrogel‐tissue chemistry 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 on understanding the structure and function of the brain in health and disease.