The object of the neurosurgeons daily endeavour, the human brain, is less well understood in its overall organization than any other organ. This puts the neurosurgeon in a very difficult position. However, a substantial body of knowledge has been accumulated during recent years, and scientists from a variety of different disciplines have worked out theoretical frameworks to accomodate the available data. Here we present some of the evolving concepts on the organization of the substrate of the mind. Review of the literature shows that application of mathematical neural network models to the nervous system is very successful in explaining function. An implicit aspect of neural network models is that information storage is not localized in certain neurons but that the information is stored as the global pattern of activity in the network. Because networks of the brain involve often millions of neurons, exact identification and comparison with the theoretical models is not possible today.