Alpha envelope detection and distortion. A polyphase rectifier circuit

An alpha modulation index for electroencephalographic studies using complex demodulation

An automated technique for measuring the relative amount of amplitude modulation of electroencephalographic (EEG) alpha activity is developed to increase the number of existing tools for differentiating the various types of alpha activity. EEG data collected from 12 normal males is used to characterize alpha modulation frequency characteristics. From these findings, a complex demodulation method is constructed to extract the amplitude modulation envelope of alpha activity from an epoch of EEG data while disregarding both continuous amplitude alpha activity and activity outside the alpha band. A threshold technique is then used to determine the relative amount of modulation contained within the data epoch. This metric is termed the alpha modulation index (AMI). Good correlation (R2 = 0.86) is found when automated scoring results are compared with manual scoring of physiologic EEG alpha modulation. The flexibility of this technique makes it easily adaptable to other EEG frequency bands and applications.