Fig 7. Representative spectrograms from three different rats.

For each rat the top trace shows the saline control injection, while the bottom trace shows the caffeine spectrogram. Scalp EEG electrodes were placed after rats were anesthetized under 2% isoflurane for at least 10 minutes. Spectrograms are shown starting 2 minutes before saline or caffeine (37.5 mg/kg) injection until the recovery of righting reflex (as shown in the artifacts caused by the motion). These spectrograms demonstrated that caffeine injection elicited significant higher frequency EEG activity compared to saline controls even though the injection took place at 2% isoflurane. Caffeine reduced the burst suppression caused by higher concentrations of isoflurane immediately after caffeine injection. As isoflurane concentrations were reduced, caffeine caused an elevation of high frequency activity earlier than saline.