Using information from concurrent EEG and fMRI, our method permitted separating and charactering the activity of the ventral attention, the dorsal attention, the core, the visual and the sensory-motor networks, as previously defined in neuroimaging studies on active and passive behavioral tasks (Corbetta and Shulman, 2002; Dosenbach et al., 2006; Fox et al., 2006; Nir et al., 2006). Among them, the first two proved to be consistently related to target detection processes. The ventral attention network included brain areas that were activated by the presentation of the rare stimuli, and other areas that were concurrently deactivated. Activation in the ventral attention system was associated with the detection of behaviorally relevant and unexpected stimuli, and, more generally, of changes in the sensory environment (Corbetta and Shulman, 2002; Downar et al., 2000). It was reported to be independent of the presentation modality, and to be significantly right-lateralized (Downar et al., 2000). The same set of brain areas was also specifically and consistently found to be associated with transient responses at task onset and offset (Fox et al., 2005; Konishi et al., 2001),
