It is often remarked that the digital age has revolutionised our access to information. But, it has also revolutionised the access of information to us. That second revolution is arguably greater, for though we spend a little more time in front of screens today compared with 20 years ago, the screens we faced then, unlike the interactive machines we face now, could not watch us back. Google is the most successful advertising platform not because it reaches so many of us, but because it knows so much about us. To put it neuroanatomically, it is the efferent, not the afferent limb …