How do primates, including humans, tell faces apart? Scientists have long attributed this ability to so-called “face-detector” (FD) neurons, thought to be responsible for distinguishing faces, among other objects. But no direct evidence has supported this claim. Now, using optogenetics, a technique that controls neural activity with light, MIT researchers have provided the first evidence that directly links FD neurons to face-discrimination in primates — specifically, differentiating between males and females. Read More...