Certainly many, perhaps even most, imaging studies have been concerned with anatomical issues. As Figure 2 illustrates, several functions of attention have been shown to involve specific anatomical areas that carry out important functions.

Imaging data have supported the presence of three networks related to different aspects of attention (Fan et al. 2005). These networks carry out the functions of alerting, orienting, and executive attention (Posner & Fan 2007). A summary of the anatomy and chemical modulators involved in the three networks is shown in Table 1. Alerting is defined as achieving and maintaining a state of high sensitivity to incoming stimuli; orienting is the selection of information from sensory input; and executive attention involves mechanisms for monitoring and resolving con.ict among thoughts, feelings, and responses.