The Believing Brain - Michael Shermer [70]
The reason dualism is intuitive and monism counterintuitive is that the brain does not perceive the process of binding all the neural networks into one whole self, and so imputes mental activity to a separate source. Hallucinations of preternatural beings such as ghosts, gods, angels, and aliens are perceived as real entities; out-of-body and near-death experiences are processed as external events; and the pattern of information that is our memories, personality, and self is sensed as a soul. The renowned neurologist and author Oliver Sacks, best known for his remarkable work in “awakening” the catatonic brains of encephalitis victims as portrayed in the popular 1990 film Awakenings starring Robin Williams, has written a number of books describing the bizarre hallucinations experienced by his patients—such as the man who mistook his wife for a hat—which are inevitably interpreted by the experiencers as external to their brain.29
One elderly patient who suffered from macular degeneration and had completely lost her vision was diagnosed by Sacks with Charles Bonnett syndrome (named for the eighteenth-century Swiss naturalist who first described it), because of her suite of complex visual hallucinations, including and especially faces with distorted teeth and eyes. Another patient developed a tumor in her visual cortex and soon after began hallucinating cartoon characters and even Kermit the Frog that were transparent and covered only half of her visual field. In fact, said Sacks, about 10 percent of visually impaired people experience visual hallucinations; faces (especially distorted faces) are the most common, cartoons are second, and geometric shapes are third. What is going on here?
In the past several years it has been possible to scan the brains of some of these patients inside a functional magnetic resonance imaging (fMRI) machine while they are hallucinating. Not surprising, the visual cortex is activated during these phantasms. During geometric hallucinations it is the primary visual cortex that is most active—the part of the brain that perceives patterns but not images. Hallucinations that include images such as faces are, not surprisingly, associated with more activity in the temporal lobe’s fusiform gyrus, which as we saw is involved in the recognition of faces. In fact, people with damage to this area cannot recognize faces, and stimulation of the fusiform gyrus causes people to spontaneously see faces. There is even a tiny portion of the fusiform gyrus dedicated to perceiving eyes and teeth, and during the hallucinations experienced by Charles Bonnett syndrome patients it is this part of the brain that is active. In another part of the brain called the inferotemporal cortex, fragments of images—thousands and even millions of fragmentary images—are all stored in individual neurons or small clusters of neurons.
“Normally, this is part of the integrated stream of perception or imagination, and one is not conscious of them,” Sacks explained. “If you become visually impaired or blind, the process is interrupted and instead of getting the smoothly organized perception, you are getting an anarchic release of activity from lots of these cells or cell clusters in the inferotemporal cortex and suddenly you start seeing fragments. The mind does its best to organize the fragments and give some coherence to it.”30
Why does the brain bother to do any of this? As Sacks told one of his patients, who insisted that she was neither crazy nor demented, “As you lose vision, as the visual parts of the brain are no longer getting any inputs from the outside world, they