The correct functioning of the mammalian brain depends on the integrated activity of myriad neuronal and non-neuronal cells. Discrete areas serve discrete functions, and dispersed or distributed communities of cells serve others. Throughout, these networks of activity are under the control of neuromodulatory systems. One goal of current neuroscientific research is to elucidate the precise methods by which these systems operate, especially during normal conscious behaviours and processes. Mircea Steriade and Denis Pare describe the neuronal properties and networks that exist within and between...