Fig. 2. Mean pain scores for the three drug conditions for pain intensity (A ) and pain averseness (B ). Mean pain scores (n = 8) are plotted with error bars  showing the SEM. At 50 ng/ml ketamine, there is a small, nonsignificant decrease in pain intensity and pain averseness. The decrease at 200 ng/ml ketamine is statistically significant (intensity, P = 0.004; averseness, P = 0.004 compared with saline). * Statistically significant decrease in pain score in comparison with saline.