Figure 1. Time line of the study plotted against the predicted effect-site concentration of thiopental (labeled THP conc in the inset graph) from an actual volunteer's data over the course of the entire study. The times of blood sampling are indicated by the up-pointing triangles. The highest target concentration (third target, or TC3) is designated as MaxTarget. For thiopental or fentanyl, the final target concentration (TC5) was actually at a time when serum concentrations were decreasing slowly (less than 20% over 1 h, in the range of pharmacokinetic variability). For propofol and midazolam, the final target concentration was held constant. Some drug was present during delayed recall/recognition testing. The inset graph shows the sequence of memory and mood tests (down-pointing triangles) during a given target concentration and baseline testing. S1, S2, S3: Sedation scales obtained in conjunction with blood samples. M1: Auditory-verbal memory test (list of 16 words) presented and repeated four times. M2: Interference task (digit span). IR: immediate recall of the list of words. DR: Delayed recall of the list of words. M3: Picture memory test (six pictures shown for 30 s each, recall delayed until end of study).