Fig. 4. D-Flandrin time–frequency distributions for one representative patient at four different measuring points: after opioid infusion ( A ), after intubation ( B ), 9 min before extubation ( C ), and 6 min before extubation ( D ). Stimulus-locked high-frequency oscillations in the time range of 15–35 ms of auditory evoked potentials are decreased during different levels of anesthesia.