cortex is very active, and the EEG reflects vigorous activity. When asleep or under general anesthesia, the pattern of activity changes. Overall, there is a change from higher-frequency signals to lower-frequency signals (which can be shown by Fourier analysis), and there is a tendency for signal correlation from different parts of the cortex to become more random.

As with other types of EEG analysis, the calculation algorithm that the BIS monitor uses is proprietary, although it has been successfully