The Brain: The Mystery of Consciousness

You exist, right? Prove it. How 100 billion jabbering neurons create the knowledge--or illusion--that you're here

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Illustration for TIME by Istvan Orosz

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And consciousness can be pushed around by physical manipulations. Electrical stimulation of the brain during surgery can cause a person to have hallucinations that are indistinguishable from reality, such as a song playing in the room or a childhood birthday party. Chemicals that affect the brain, from caffeine and alcohol to Prozac and LSD, can profoundly alter how people think, feel and see. Surgery that severs the corpus callosum, separating the two hemispheres (a treatment for epilepsy), spawns two consciousnesses within the same skull, as if the soul could be cleaved in two with a knife.

And when the physiological activity of the brain ceases, as far as anyone can tell the person's consciousness goes out of existence. Attempts to contact the souls of the dead (a pursuit of serious scientists a century ago) turned up only cheap magic tricks, and near death experiences are not the eyewitness reports of a soul parting company from the body but symptoms of oxygen starvation in the eyes and brain. In September, a team of Swiss neuroscientists reported that they could turn out-of-body experiences on and off by stimulating the part of the brain in which vision and bodily sensations converge.

THE ILLUSION OF CONTROL

ANOTHER STARTLING CONCLUSION FROM the science of consciousness is that the intuitive feeling we have that there's an executive "I" that sits in a control room of our brain, scanning the screens of the senses and pushing the buttons of the muscles, is an illusion. Consciousness turns out to consist of a maelstrom of events distributed across the brain. These events compete for attention, and as one process outshouts the others, the brain rationalizes the outcome after the fact and concocts the impression that a single self was in charge all along.

Take the famous cognitive-dissonance experiments. When an experimenter got people to endure electric shocks in a sham experiment on learning, those who were given a good rationale ("It will help scientists understand learning") rated the shocks as more painful than the ones given a feeble rationale ("We're curious.") Presumably, it's because the second group would have felt foolish to have suffered for no good reason. Yet when these people were asked why they agreed to be shocked, they offered bogus reasons of their own in all sincerity, like "I used to mess around with radios and got used to electric shocks."

It's not only decisions in sketchy circumstances that get rationalized but also the texture of our immediate experience. We all feel we are conscious of a rich and detailed world in front of our eyes. Yet outside the dead center of our gaze, vision is amazingly coarse. Just try holding your hand a few inches from your line of sight and counting your fingers. And if someone removed and reinserted an object every time you blinked (which experimenters can simulate by flashing two pictures in rapid sequence), you would be hard pressed to notice the change. Ordinarily, our eyes flit from place to place, alighting on whichever object needs our attention on a need-to-know basis. This fools us into thinking that wall-to-wall detail was there all along--an example of how we overestimate the scope and power of our own consciousness.

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