Seeing gender
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. Working with macaque monkeys trained to correctly identify images of male or female faces, the researchers used a light-sensitive protein to suppress subregions of FD neurons in the inferior temporal (IT) cortex, a visual information-processing region. In suppressing the neurons, the researchers observed a small yet significant impairment in the animals’ ability to properly identify genders. “If these face-detector neurons are participating in face-discriminating behavior — in telling gender of faces apart — then, if we knock them down, the behavior should take...