As Charles Bell noted back in 1830, his patients most frequently suffered phantom limb phenomena if they had completely lost an arm or leg. And the amputee’s vivid, ongoing illusion—that this missing limb is still attached—is so convincing that it can set the stage for delusions. Admiral Horatio Nelson, whose right arm had been amputated after the battle of Tenerife, became so attached to the illusion that he took his persistent phantom arm as compelling evidence that his soul, too, would be eternal in nature. Zen has long emphasized that our delusions also build on illusions.

From James H. Austin’s Zen and the Brain, Cambridge, Massachusetts: The MIT Press, 1999 (first published in 1998), p. 398.