Fig. 1. Criteria used to differentiate between stimulus intensity–dependent (  A ) and –independent rostral trigeminal sensory nuclear complex (TNSC) neurons and to identify trigeminothalamic neurons (  B ). (  A ) Graphs illustrate the response profile of stimulus intensity–-dependent and –independent neurons in response to tooth-pulp stimulation. The evoked activity (spikes/stimulus) of stimulus intensity–dependent neurons increases if graded electrical stimuli are applied to the canine tooth pulp. In contrast, the activity of stimulus intensity–independent neurons is not affected by similar graded stimuli. Each point on the graphs represents the mean ± SD, n = 50 trials. (  B ) Five superimposed oscilloscope traces are presented of an air puff–evoked TSNC neuron responding to high-frequency stimuli (0.2 ms, 140 μA, 500 Hz) applied to the contralateral thalamus. A single oscilloscope trace below illustrates a collision with an ongoing action potential.  Asterisks denote the stimulus onset. The  arrow indicates the location at which the antidromic spike should have occurred. Antidromic latency: 1.3 ms.