Measure what is measurable, and make measurable what is not so.
This quote from Galileo Galilei, one of the founding fathers of science, is a call to arms for ingenious bench scientists, clinicians and theoreticians to render consciousness measurable: to build an instrument that can tell whether that prone person who is nonresponsive or behaving in a reflexlike manner is actually conscious of something—of anything. Such a “consciousness meter” should reliably distinguish between a sleeper who is experiencing a vivid dream—even if she does not recall most of its content later on—and one who is in a dreamless, deep sleep, not feeling anything. Not just black but nothing, nichts, nada, rien. Or between a patient who is deeply anesthetized, and oblivious to the abdominal surgery being performed on him, and the rare cases of “awareness under anesthesia.” Such a device should also be able to tell whether a grievously brain-injured patient, whose electroencephalograph (EEG) might be flat but who is moaning and occasionally moving his head or limbs, is experiencing pain or distress or is truly not conscious—alive but oblivious to the world.