Fig. 2. Cortical activation in anterior cingulate cortex (top ), thalamus (middle ), and cerebellum (bottom ) evoked by noxious heat stimulation during alert control and target propofol concentrations of 0.5 μg/ml (mild sedation), 1.5 μg/ml (moderate sedation), and 3.5 μg/ml (unconsciousness). All images show subtractions of noxious heat minus warm. The left side of the images corresponds to the left side of the brain. The color scale shows t values are between 2.0 and 4.0.