An alpha modulation index for electroencephalographic studies using complex demodulation

An automated technique for measuring the relative amount of amplitude modul ation of electroencephalographic (EEG) alpha activity is developed to incre ase the number of existing tools for differentiating the various types of a lpha activity EEG data collected from 12 normal males is used to characteri ze alpha modulation frequency characteristics. From these findings, a compl ex demodulation method is constructed to extract the amplitude modulation e nvelope 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 modul ation contained within the data epoch. This metric is termed the alpha modu lation index (AMI). Good correlation (R-2 = 0.86) is found when automated s coring results are compared with manual scoring of physiologic EEG alpha mo dulation. The flexibility of this technique makes it easily adaptable to ot her EEG frequency bands and applications.