Incognito: The Secret Lives of the Brain

by David Eagleman

Consider Joan of Arc, the sixteen-year-old-girl who managed to turn the tide of the Hundred Years War because she believed (and convinced the French soldiers) that she was hearing voices from Saint Michael the archangel, Saint Catherine of Alexandria, Saint Margaret, and Saint Gabriel. As she described her experience, “When I was thirteen, I had a voice from God to help me to govern myself. The first time, I was terrified. The voice came to me about noon: it was summer, and I was in my father’s garden.” Later she reported, “Since God had commanded me to go, I must do it. And since God had commanded it, had I had a hundred fathers and a hundred mothers, and had I been a king’s daughter, I would have gone.” Although it’s impossible to retrospectively diagnose with certainty, her typical reports, increasing religiosity, and ongoing voices are certainly consistent with temporal lobe epilepsy. When brain activity is kindled in the right spot, people hear voices. If a physician prescribes an anti-epileptic medication, the seizures go away and the voices disappear. Our reality depends on what our biology is up to.