Figure 31-20 Schematic diagram of signal processing paths integral to generating a single bispectral (BIS) index value. After digitization and artifact rejection, original electroencephalographic (EEG) epochs undergo three primary paths of analysis—power spectral analysis, BIS analysis, and time-based analysis for suppression/near suppression—to look for key EEG features. The BIS algorithm, based on statistical modeling, combines the contributions of each of the identified features to generate the scaled BIS index. (Redrawn from Kelley SD: Monitoring Level of Consciousness during Anesthesia and Sedation. Natick, MA, Aspect Medical Systems, 2003.)