In the last decade, it has been possible to trace the areas of the human brain involved in a variety of cognitive and emotional processes by use of imaging technology. Brain networks that subserve attention have been described. It is now possible to use these networks as model systems for the exploration of symptoms arising from various forms of pathology. For example, we can use the orienting network to understand the effects of lesions that produce neglect of sensory information either by brain damage or by restricting transmitter input. Frontal attention networks may provide similar understanding of pathologies at higher levels of cognition. Evidence relating these networks to attention deficit and hyperactivity disorder (ADHD) is considered.