Fig. 3. Methylphenidate-induced electroencephalogram changes during continuous inhalation of isoflurane are inhibited by droperidol. Thirty-second epochs of electroencephalogram recordings from a single rat show the change from an active, θ-dominant pattern during the awake state to the δ-dominant pattern during inhalation of isoflurane (1.0%). The latter pattern is unchanged after the administration of normal saline. Administration of intravenous (IV) methylphenidate (5 mg/kg) induced a prompt shift in the electroencephalogram back to an active θ-dominant pattern similar to that observed during the awake state. This pattern persisted for more than 15 min (A ). Thirty-second epochs of raw electroencephalogram recordings from a different animal than in A  show the same patterns during the awake and anesthetized states (B ). Administration of IV droperidol (0.5 mg/kg) induced no appreciable change in the electroencephalogram pattern. However, when IV methylphenidate (5 mg/kg) was administered 5 min after droperidol, the electroencephalogram did not return to the active, θ-dominant pattern observed during the awake state. Rather, the δ-dominant pattern persisted.