Fig. 6. Interstimulus interval (ISI ) duration during 0.79 MAC (the minimum alveolar concentration producing immobility in 50% of subjects receiving noxious stimulation) isoflurane influences electromyographic responses (results for one animal). By 33 s of stimulation with 3-s ISI pulses, electromyographic activity develops after each pulse but then fades and movement does not occur. During stimulation with shorter ISI pulses, the latency to electromyographic activation decreases and movement occurs. Stimulation was discontinued after movement occurred.