Fig. 4. Effect of ketamine on a stimulus intensity–independent trigeminal sensory nuclear complex neuron. Oscilloscope traces represent behavioral state, and poststimulus time histograms reflecting neuronal activity were constructed as described in  fig. 3 . Neuronal activity was evoked by low-intensity bipolar electrical stimuli applied to the canine tooth pulps (0.2 ms, 8.0 μA, 1.0 Hz). The number above each histogram indicates the mean (± SD) evoked activity, in spikes per stimulus. Note that tooth pulp–evoked activity in this neuron was reversibly suppressed by 24% during ketamine anesthesia. Vertical calibration bars (electroencephalogram, electrooculogram, pontogeniculooccipital wave, electromyogram): 50 μV.