Key pointsr The mechanisms of action of anaesthetics on the living brain are still poorly understood.In this respect, the analysis of the differential effects of anaesthetics on spontaneous and sensory-evoked cortical activity might provide important and novel cues.r Here we show that the anaesthetic sevoflurane strongly silences the brain but potentiates in a dose-and frequency-dependent manner the cortical visual response. Abstract General anaesthetics, which are expected to silence brain activity, often spare sensory responses. To evaluate differential effects of anaesthetics on spontaneous and sensory-evoked cortical activity, we characterized their modulation by sevoflurane and propofol. Power spectra and the bust-suppression ratio from EEG data were used to evaluate anaesthesia depth. ON and OFF cortical responses were elicited by light pulses of variable intensity, duration and frequency, during light and deep states of anaesthesia. Both anaesthetics reduced spontaneous cortical activity but sevoflurane greatly enhanced while propofol diminished the ON visual response. Interestingly, the large potentiation of the ON visual response by sevoflurane was found to represent a linear scaling of the encoding mechanism for light intensity. To the contrary, the OFF cortical visual response was depressed by both anaesthetics. The selective depression of the OFF component by sevoflurane could be converted into a robust potentiation by the pharmacological blockade of the ON pathway, suggesting that the temporal order of ON and OFF responses leads to a depression of the latter. This hypothesis agrees with the finding that the enhancement of the ON response was converted into a depression by increasing the frequency of light-pulse stimulation from 0.1 to 1 Hz. Overall, our results support the view that inactivity-dependent modulation of cortical circuits produces an increase in their responsiveness. Among the implications of our findings, the silencing of cortical circuits can boost linearly the cortical responsiveness but with negative impact on their frequency transfer and with a loss of the information content of the sensory signal.
Magnetic resonance imaging (MRI) requires patient immobility and children generally need to be sedated. The ideal sedative agent for functional MRI (fMRI) should only minimally hamper the neurophysiologic effect of the administered sensorial stimulation. This study compares the effect of propofol and midazolam on the fMRI auditory activation pattern in children. Fourteen children in the 3 to 7 year age group without neurologic or auditory deficits were randomly assigned to receive propofol or midazolam for sedation during auditory fMRI. Two patients in the midazolam group were excluded due to positive baseline MRIs. The children were stimulated using a passive listening task. The fMRI signal was modeled using various functions (hemodynamic response function, temporal derivative, and dispersion derivative) to check for the differing temporal characteristics of the signal between the groups. Patients in the propofol group showed activation only in the primary auditory cortex and exhibited a pattern more similar to that of nonsedated adults. Patients in the midazolam group exhibited a more complex pattern, presenting activation areas other than the primary auditory cortex; a delay in the functional response and higher duration variability were also observed. Our sample sizes are too small to derive a conclusive inference. Our preliminary study encourages the hypothesis that propofol is preferable to midazolam to maintain sedation in 3 to 7-year-old children during auditory fMRI because it facilitates the elicitation of a more focused auditory cortical activation pattern with less temporal and spatial dispersion.
After auditory stimuli, propofol-sedated 5- to 8-year-old children exhibit an fMRI cortical activation pattern which is different from that in similarly aged nonsedated children.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.