Fig. 5. Summary of ketamine's action on stimulus intensity–independent trigeminal sensory nuclear complex neurons (n = 8). The graph was constructed as described in  fig. 4 . Overall, tooth pulp–evoked activity at threshold was suppressed 33%, 5 min after the onset of drug administration. Mean evoked activity returned to control levels (indicated by the  dashed line ) approximately 30 min after ketamine infusion.  Asterisks indicate statistically significant differences from control (  P < 0.05 on repeated-measures analysis of variance, Dunnett's method). Error bars =± SD.