Figure 5. Example of pain ratings (upper graph) in response to intracutaneous electrical stimuli before and after administration of 0.5 mg *symbol* kg-1ketamine in one subject. After ketamine injection, the subject became unconscious, and no pain ratings could be obtained for 10 min. In contrast, SEP were attenuated but still recordable. On awakening, pain ratings were lower when compared with the premedication level during the whole observation period. This long-lasting analgesic effect was reflected by a comparable decrease in the amplitude of the cerebral potential.