Figure 2. Upper graphs: Mean power spectral density (PSD) functions of spontaneous electroencephalogram activity in three subjects before and after medication (bandpass: 0.5–30 Hz; epoch length: 5 s; the single-trial spectra were smoothed by a running median filter and a moving average filter, each with a length of 5 points). The injections were given 10 min after start of recordings. Bottom: Iso-contour line plots representing different levels of the PSD functions given above. The lowest iso-contour line corresponds to a power spectral density of 20% above the mean power in the premedication period. The difference between two successive contour lines amounts to 0.25 micro Volt²/Hz. Alpha activity was dominant over time in the placebo group. After ketamine injection, alpha activity was transiently replaced by a dose-dependent increase in theta activity.