Fig. 1. Schematic representation of the experimental protocol. The stimulus (visual search task vs.  baseline task) was presented during three epochs corresponding to the following experimental conditions: baseline condition, isoflurane condition, and recovery condition. During each experimental condition, five blocks of the baseline task were presented in an interleaved manner with five blocks of the visual search task. The duration of each block was 30 s. Functional magnetic resonance imaging (fMRI) data were continuously acquired during the entire experiment. As a representative example we show a typical fMRI signal response of a single voxel in the visual cortex. It was obtained by multisubject averaging over the isoflurane group. Note how the fMRI signal follows the switching on and off of the external stimulus.