This second edition of our book was written 20 years after the first. There have been great technological advances made during this period, advances that now make possible the recording of additional physiological measures from brain and periphery under a variety of conditions not thought possible when we wrote the first edition. Consider the fact that functional magnetic resonance imaging (fMRI) is now being used in several laboratories to monitor changes in blood flow in the brain, and on a recent NASA mission the electrogastrogram (EGG) was used to measure gastric myoelectric activity from a freely moving astronaut in zero gravity
