Figure 1. Changes in spontaneous cortical activity induced by sevoflurane and propofol.

A, spontaneous cortical voltage oscillations observed in an exemplar experiment where the animal was exposed to three different concentrations of sevoflurane (top; 2.5, 3.75 and 5%) and propofol (bottom; 1, 1.5 and 2 mg kg⁻¹ min⁻¹; traces from the same rat kept in the dark and exposed to the two different anaesthetics in consecutive experimental sessions, 3 days apart). Notice the dose‐dependent change in spontaneous activity with a burst‐suppression pattern for the intermediate and highest anaesthetics doses. B, BSR for both anaesthetics at all dosages (n = 7 rats exposed to both agents). C and D, average periodograms from three representative unfiltered EEG recordings (10 s sweeps, total trace length 110 s) obtained as above for sevoflurane (2.5, 3.75 and 5%; C) and propofol (1, 1.5 and 2 mg kg⁻¹ min⁻¹; D). The sharp peak at 50 Hz in D is from power‐line noise. E and F, mean PSD from quantitative spectral analysis for sevoflurane (E) and propofol (F), on the whole frequency band (0.5–80 Hz; left in both panels E and F) and for single frequency bands (right in both panels E and F) as a function of anaesthetic dosage (n = 7, animals exposed to both anaesthetics). Asterisks indicate significance values (panel B, principal effect by Friedman test; panels E and F, principal effect by one‐way rANOVA; P > 0.05, ns; ^* P < 0.05; ^** P < 0.01; ^*** P < 0.001).