Some scientists, sociologists and economists in particular, recently gave a second sense to the terms "social cognition" used by psychologists, namely a cognition distributed over the whole set of the individuals composing a society. The stake is then to know "in what extent the human social aptitudes account for the development of a complex collective cognition". We defend here the idea that social cognition is a refinement of the concept of distributed cognition rather than an equivalent. It is a phenomenon specific to the human societies which allows to think their property of self-transformation. In this paper, we show how the study of imitation processes can help us to think this phenomenon, as suggested it in its time Gabriel Tarde.