How distributed is the brain-wide network that is recruited for cognition?

Half a century of neurophysiological recordings from single electrodes established a 'localized' viewpoint on function in the brain - that complex behaviour results from computations that are carried out and representations that occur across distinct brain areas, each of which has a specialized role. Data generated from new techniques for specific, high-throughput measurement of neuronal activity and behaviour in rodents have prompted an alternative viewpoint, which posits that neural encoding of behavioural variables is distributed across a wide range of areas: 'everything, everywhere, all at once'. After briefly introducing these paradigms, we evaluate which of them better describes cognition - the manipulation of internal variables that enables flexible behaviour. Measurements of neuronal activity in both rodents and primates suggest that cognitive variables are reflected broadly but not ubiquitously across the brain, including, to a surprising degree, in regions engaged in controlling movement. We close by discussing why cognitive signals may appear in such areas, as well as the factors that affect the breadth of the brain-wide network that is recruited for cognition.