In order to calculate the AFC, ERP are first averaged and then transformed to the frequency domain using a one-sided Fourier transform (Laplace transform).15,24 Brain oscillations in response to stimulation have helped to advance the analysis. First of all, in order to perform Fourier analysis of brain responses, an averaging procedure is applied to the data of healthy subjects and patients. Following artifact rejection, selective averaging is performed. The averaged potentials (EP and/or ERP) are then analyzed using a fast Fourier transform (FFT) and single epochs are digitally filtered based on the cut-off frequencies of the evoked power spectra. Lastly the data are averaged across subjects to produce a grand average. Another option is power spectral analysis of the grand average with adaptive digital filtering.
