Fig. 3. Peristimulus time histograms (bin width = 1 sec) of individual single-unit responses to graded noxious heat. One unit was recorded under halothane anesthesia (A , B ), and another unit was recorded under isoflurane anesthesia (C , D ), at 0.9 of the animal's individual minimum alveolar concentration (iMAC) (A , C ), and at 1.1 iMAC (B , D ). Halothane depressed the unit's response to heat when halothane concentration was increased from 0.9 to 1.1 iMAC (A , B ), whereas isoflurane slightly enhanced another unit's responses at equipotent concentrations (C , D ).