This video illustrates the basic steps required to calculate PCI and the main results obtained in sleep, anesthesia and brain-injured patients. Measuring PCI involves perturbing the brain with transcranial magnetic stimulation and recording its immediate response by means of electroencephalography. Zipping the brain's response to a magnetic perturbation to calculate its information content allows discriminating between conscious and unconscious subjects. This video relates to a paper that appeared in the August 14, 2013, issue of Science Translational Medicine, published by AAAS. The paper, by A.G. Casali at the University of Milan in Milan, Italy, and colleagues was titled, "A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior."