Fig. 2. Effect of ketamine on a stimulus intensity–dependent trigeminal sensory nuclear complex (TSNC) neuron. The first four traces represent 10-s epochs of electroencephalogram, electrooculogram, pontogeniculooccipital wave, and electromyogram activity characteristic of wakefulness, ketamine-induced anesthesia, and recovery. Below these traces are five overlaid oscilloscope traces illustrating the tooth pulp–evoked activity of this TSNC neuron. Poststimulus time histograms (PSTHs) were constructed from 50 consecutive responses evoked by threshold ( A ; 0.2 ms, 5.5 μA, 1 Hz) and suprathreshold ( B ; 0.2 ms, 6.0 μA, 1 Hz) electrical stimuli applied to the canine tooth pulp. The number above each PSTH indicates the mean (± SD) evoked activity, in spikes per stimulus. Note that in this cell, tooth pulp–evoked activity decreased 76% at threshold and 57% at suprathreshold intensity during ketamine anesthesia. Vertical calibration bars: 50 μV.