Figure 3. The effect-site concentration versus the electroencephalogram effect relation from two different volunteers show a biphasic (upper panel) and a monophasic (lower panel) response. In the volunteer with the biphasic response, the electroencephalogram reached a peak at about 1.3 mg/ml. In the other volunteer, the effect increased continuously to an effect-site concentration of 3.3 mg/ml, the highest effect-site concentration in this volunteer.