Brain metabolic mapping techniques, such as positron emis-sion tomography (PET), can provide information about the functional interactions within entire neural systems. With the large quantity of data that can accumulate from a mapping study, a network analysis, which makes sense of the com-plex interactions among neural elements, is necessary. A network analysis was performed on data obtained from a PET study that examined both the changes in regional ce-rebral blood flow (rCBF) and interregional correlations among human cortical areas during performance of an object vision (face matching) and spatial vision (dot-location matching) task. Brain areas for the network were selected based on regions showing significant rCBF or interregional correla-tions between tasks. Anterior temporal and frontal lobe regions were added to the network using a principal com-

ies, 1984) distinguishes sustained from selective attention; the first is defined as maintaining attention to a single source of information for an unbroken period of time, whereas the second is defined as attending to one source of information and excluding the others. Both sustained and selective attention are affected by the level of arousal (Das et al., 1994). The link between attention and arousal is related to their mutual dependency and complementary behavioral expression (Lynn, 1966). A correlation between performance of attentional tasks and level of arousal has been reported (Babkoff et al., 1991). However, arousal and attention are related in a nonlinear manner: attentional performance improves with a moderate increase of arousal but drops dramatically when a state of high excitement is reached (Easterbrook, 1959). On the other hand, sustained attention reduces arousal and induces drowsiness (Babkoff et al., 1991). Arousal and attention rely on distinct anatomical systems

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