Fig. 6. Individual examples showing relation among simultaneously-recorded stimulus temperature (top ), withdrawal force (middle ) and unit responses (bottom , raw trace) for one unit recorded under halothane anesthesia (A , B ) and another unit recorded under isoflurane anesthesia (C , D ). Unit responses to 51 and 55°C stimuli are shown at 0.9 of the animal's individual minimum alveolar concentration (iMAC) (A , C ) and at 1.1 iMAC (B , D ) for halothane and isoflurane, respectively. Absence of a withdrawal response was accompanied by a reduction in the number of impulses discharged under halothane (A , B ), but not for isoflurane (C , D ). Note that spike amplitude remained stable throughout withdrawal responses. Temperature tracings at top show thermode temperatures (solid line ) and intradermal temperatures (dotted line ), rising from a baseline temperature of 35°C. Intradermal temperatures were taken from pilot experiments in another animal. The number of impulses discharged during the heat stimulus and during the 60-s period following the onset of heat, for each response, is superimposed over the raw unit traces (bottom ).