Fig. 6. Mean stimulus–response functions for the area under the curve (AUC) of withdrawal force. Withdrawal force was significantly depressed by isoflurane from 0.65 to 0.85 minimum alveolar concentration (MAC) (P < 0.001) and abolished at 1.15 MAC, except for two animals that showed small withdrawals to the highest stimulus intensity. Fractions indicate the proportion of trials in which an animal exhibited a withdrawal (for each of 21 neurons in 19 animals), at each stimulus temperature and each MAC concentration. Withdrawal incidence was dose-dependently decreased by isoflurane. Error bars = SEM. * Significantly less than withdrawal force at 0.65 MAC across all stimulus temperatures.