The Believing Brain - Michael Shermer [57]
The mismatch between your body schema and the artificially induced doppelgänger probably occurs between the parietal lobe and the temporal lobe in your brain. Specifically, it is the job of the posterior superior parietal lobe to orient your body in physical space (the back and upper regions of this lobe sit above and to the rear of the temporal lobe above your ears). This is the part of the brain that can tell the difference between you and not-you, which is to say everything else outside of your body. When this part of the brain is quiescent during deep meditation and prayer (as witnessed in brain scan studies), subjects (Buddhist monks and Catholic nuns) report feeling at one with the world or in deep contact with the transcendent.31 In a manner of speaking, meditation and prayer have created a mismatch between the body schema and the world, and it is possible that something like this happens under extreme and unusual conditions.
Phantom limbs are another perceptual mismatch. At the University of California–San Diego, the neuroscientist V. S. Ramachandran (“Rama”) has used the concept of the body schema to treat phantom pain in patients who have lost an arm. Essentially, these patients are suffering from a limb schema mismatch, with their eyes reporting that there is no limb while their body schema still maintains the limb image. Why this should result in pain is not clear. Rama suggests several explanations, including irritation of the nerve endings, central remapping (leading to referred sensations) in which “some low threshold touch input might cross-activate high threshold pain neurons,” and a “mismatch between motor commands and the ‘expected’ but missing visual and proprioceptive input” that “may be perceived as pain.”32 Whatever the cause, the patient’s brain sends a signal to the phantom arm to move, but the signal sent back to the brain is that it can’t move (patients report feeling as if their arm is “stuck in cement” or “frozen in a block of ice”), and thus there is a “learned paralysis.” To correct the mismatch, Rama constructed a mirror box. The patient inserted his left phantom arm into one side of the box behind the mirror and his right intact arm into the other side. The mirror reflected the right whole arm as a mirror image of the left phantom arm. Rama then had the man wiggle the fingers of the right arm, which sent signals back to his brain that the phantom arm was moving, thereby overriding the learned paralysis and leading to a dramatic reduction of phantom pain.33
Phantom limbs, body schemas, and visual and auditory hallucinations are all neural correlates of the dualistic stance that mind and body exist as separate agents both in ourselves and others, and we thereby attribute intentional agency not only to real others but to phantom others as well.
4. A conflict within the mind schema, or our psychological sense of self, in which the mind is tricked into thinking that there is another mind. Our brains consist of many independent neural networks that at any given moment are working away at various problems in daily living. And yet we do not feel like we’re a bundle of networks. We feel like a single mind in one brain. The neuroscientist Michael Gazzaniga thinks that we have a neural network that coordinates all the other neural networks and weaves them together into a whole. He calls this the left-hemisphere interpreter, the brain’s storyteller that puts together countless inputs into a meaningful narrative story. Gazzaniga discovered this network while studying split-brain patients whose hemispheres have been separated to stop the spread of epileptic seizures. In one experiment, Gazzaniga presented the word walk to only the right hemisphere of a split-brain