The neural oscillations that underlie ERPs are called EROs. Although EROs are measured in the same frequency bands as spontaneous resting EEGs— namely, delta (1–3 Hz), theta (3.5–7.5 Hz), alpha (8.0–11.5 Hz), beta (12–28 Hz), and gamma (28.5–50.0 Hz)—functionally they are different from spontaneous resting EEG rhythms. EROs temporally are related to the sensory and cognitive processing of stimuli (Basar et al. 1999). During sensory reception, groups of neurons that are close together fire together at fast rates in the gamma range. Cognitive processing (e.g., attention to an auditory rather than a visual stimulus), however, involves communication between brain regions that are somewhat farther apart (e.g., adjacent temporal and parietal lobes [figure 1]). This processing involves synchronization between the brain regions in the alpha and beta frequency ranges. Higher cognitive processing (e.g., working memory, determining if a stimulus has been seen before) involves interactions between widely separated brain regions (e.g., frontal and parietal lobes [figure 1]). Higher cognitive processing involves slow synchronization in the theta or delta frequency range (Lubar 1997). Thus, faster frequencies represent synchronization of groups of neurons
