The diversity of behaviors across the animal kingdom is staggering, from feats of agility to nuanced social interactions. Ultimately, these complex behaviors arise from the chatter of neurons, and cracking their “code” has driven systems neuroscience for decades. Indeed, since the 1960s, two observations have captivated neuroscientists. First, the performance of even simple tasks, such as looking at a flash of light, evokes activity in many neighboring neurons. Is this merely built-in redundancy, or does it hint at a more distributed code? Second, individual neurons respond to large numbers of features, such as the color and shape of visual stimuli. Does this “mixed selectivity” reflect ingrained properties of neural function, or is it epiphenomenal?
A body of recent work has suggested a parsimonious explanation for these observations: Perhaps information is not uniquely encoded in the spike trains of individual neurons but rather specified by the coordinated activity of neural populations. By analogy, each of the individual words in this article has meaning, but the information therein becomes clear only when considering all the words together.