The vigilance-controlled quantified EEG can be used either as a safety, or as a discovery pharmacology procedure. Put strategically into the preclinical development process of a drug, it can be useful for making the decision about the future research direction to be taken. The experimental approach described in this unit is based on the rat EEG. Even though there are considerable differences in function and structure between human and rat brain, the EEG response to psychoactive drugs and convulsants is similar in the two species. Thus, the rat EEG is generally a reliable predictor for human CNS drug effects.