Propofol induced unconsciousness: fMRI total neuronal activity and resting state networks

• ¹ University of Liège, Cyclotron Research Centre, Belgium

Objectives: To date, there is no consensus on the mechanisms by which anesthetic drugs induce loss of consciousness (Brown et al., 2010). Resting state fMRI studies have identified several brain networks including the default mode network, executive control networks, auditory and visual networks (Damoiseaux et al., 2006). Our aim was to analyze the effects of propofol anesthesia by investigating changes in relevant resting state networks functional connectivity patterns and in a total neuronal single scalar map obtained combining all resting state networks of neuronal origin.

Methods: Data from 18 healthy participants were acquired at resting state in four conditions: wakefulness, mild sedation, deep sedation and recovery of consciousness, using 3T-fMRI. Independent component analysis identified 30 components which were tested for neuronality using both temporal and spatial properties. All neuronal components were then combined to create scalar maps of total neuronal activity. A repeated measures general linear model (random effects analysis) tested for significant differences between conditions. In a second analysis we selected 7 relevant networks through template matching, that had significant activation over all four conditions and we examined their pattern of activity across conditions.

Results: Analysis of the scalar maps revealed a significant decrease in resting state total neuronal activation with loss of consciousness and several areas in the prefrontal, parietal and temporal lobe that correlated negatively with the state of consciousness (p<0.03 whole brain FWE correction, Figure 1). The default mode and bilateral executive control networks correlated negatively with state of consciousness, whereas left and right visual networks stayed stable over the conditions. The sensorimotor and auditory network showed a paradoxical effect of increased thalamic activity with mild sedation.

Conclusion: The creation of a single total neuronal scalar map made it possible to identify regions in the whole brain that are modified by propofol. While primary processing networks remain active in decreased levels of awareness, higher order functioning networks become disintegrated. Our findings suggest that functioning in higher order fronto-parietal networks is diminished through anesthesia, leading to loss of consciousness.