Neurosciences New Toolbox

With the invention of optogenetics and other technologies, researchers can investigate the source of emotions, memory, and consciousness for the first time.

The hypothalamus is a small structure deep in the brain that, among other functions, cordinates sensory inputsthe appearance of a rival, for examplewith instinctual behavioral responses. Back in the 1920s, Walter Hess of the University of Zurich (who would win a Nobel in 1949) had shown that if you stuck an electrode into the brain of a cat and electrically stimulated certain regions of the hypothalamus, you could turn a purring feline into a furry blur of aggression. Several interesting hypotheses tried to explain how and why that happened, but there was no way to test them. Like a lot of fundamental questions in brain science, the mystery of aggression didnt go away over the past centuryit just hit the usual empirical roadblocks. We had good questions but no technology to get at the answers.