Abstract: The invention relates to a method and apparatus for monitoring the cerebral state of a subject. At least one of a first and second parameters is derived from the physiological signal data obtained from the subject, wherein the first parameter is indicative of the sum of spectral values of the physiological signal data in a first frequency band lying above high frequency EEG activity and the second parameter is indicative of the relative magnitudes of a first sum of k-th order spectral values and a second sum of n-th order spectral values. The second sum is calculated over a frequency band lying above high frequency EEG activity (k>2 and n>1). A state index is then formed, which is dependent on the at least one parameter and indicative of the cerebral state of the subject. The first and second parameters may be used in the Bispectral Index (BIS™) algorithm.

Abstract: The invention relates to a method and apparatus for monitoring the anesthetic state of a subject. Physiological signal data including EEG and possibly also EMG signal components is acquired from a subject and supplied to a monitoring process configured to derive, based on the said data, a state index indicative of the anesthetic state of the subject. In order to extend the applicability of present-day monitoring processes, the operation of the monitoring process is controlled according to whether at least one drug inducing high frequency EEG signal components is administered to the subject. The presence of the high frequency EEG signal components in the physiological signal data may be detected automatically.