This paper argues that the 'brain' has become a frequently invoked and symptomatic source of metaphorical imagery in our current technologically mediated and dominated culture, through which the distinction between the human and the technological has been and continues to be negotiated, particularly in the context of the increasing ubiquity of electronic and digital technologies. This negotiation has thrown up three distinct, though interrelated, figures. One is the 'Brain in a Vat', in which the brain can connect to and even operate solely through electronic technologies. Another is the 'Electronic' or, more archaically, 'Giant Brain', in which the brain's functions can be reproduced and exceeded by electronic computing technology. A third is the 'World' or 'Global Brain', in which the connectivity enabled by information-communications technologies produces and fosters forms of distributed intelligence. This paper will trace the development of these figures and show how they have developed in lockstep throughout the two or three centuries of exponentially accelerating technological advance.