The last century has seen great progress in our understanding of those aspects of neural computation that can be studied through experimentation on one or a few cells–for example, how synapses enable a neuron to talk to one of its neighbors. But the phenomena that got many neuroscientists interested in the brain in the first place–learning, emotion, consciousness, and mysterious disorders such as depression and schizophrenia–remain difficult to explain through experiments on just one or even a few cells. Thousands or millions of cells, computing as an ensemble, are responsible for practically all of our behaviors, as well as the derangements thereof. …