normal visual systems are blindfolded for as little as an hour, their primary visual cortex becomes active when they perform tasks with their fingers or when they hear tones or words. Removing the blindfold quickly reverts the visual cortex so that it responds only to visual input. As we’ll see more in upcoming chapters, the brain’s sudden ability to “see” with the fingers and ears depends on connections from other senses that are already there but not used so long as the eyes are sending data.
Collectively, these considerations led us to propose that visual dreams are a by-product of neural competition and the rotation of the planet. An organism that wishes to keep its visual system from takeover by the other senses must devise a way to keep the visual system active when the darkness sets in.
So now we’re ready for a question. We’ve painted the picture of an extremely flexible cortex. What are the limits of its flexibility? Can we feed any kinds of data into the brain? Would it simply figure out what to do with the data it receives?
4
WRAPPING AROUND THE INPUTS
Every man can, if he so desires, become the sculptor of his own brain.
—SANTIAGO RAMÓN Y CAJAL (1852–1934), neuroscientist and Nobel laureate
Michael Chorost was born with poor hearing, and he got by during his young adult life with the help of a hearing aid. But one afternoon, while waiting to pick up a rental car, the battery to his hearing aid died. Or so he thought. He replaced the battery but found that all sound was still missing from his world. He drove himself to the nearest emergency room and discovered that the remainder of his hearing—his thin auditory lifeline to the rest of the world—was gone for good.1
Hearing aids wouldn’t be of any use for him now; after all, they work by capturing sound from the world and blasting it at higher volume into the ailing auditory system. This strategy is effective for some types of hearing loss, but it only works if everything downstream of the eardrum is functioning. If the inner ear is defunct, no amount of amplification solves the problem. And this was Michael’s situation. It seemed as though his perception of the world’s soundscapes had come to an end.
But then he found out about a single remaining possibility, and in 2001 he underwent surgery for a cochlear implant. This tiny device circumvents the broken hardware of the inner ear to speak directly to the functioning nerve (think of it like a data cable) just beyond it. The implant is a minicomputer lodged directly into his inner ear; it receives sounds from the outside world and passes the information to the auditory nerve by means of tiny electrodes.
So the damaged part of the inner ear is bypassed, but that doesn’t mean the experience of hearing comes for free. Michael had to learn to interpret the foreign language of the electrical signals being fed to his auditory system:
When the device was turned on a month after surgery, the first sentence I heard sounded like “Zzzzzz szz szvizzz ur brfzzzzzz?” My brain gradually learned how to interpret the alien signal. Before long, “Zzzzzz szz szvizzz ur brfzzzzzz?” became “What did you have for breakfast?” After months of practice, I could use the telephone again, even converse in loud bars and cafeterias.
Although being implanted with a minicomputer sounds something like science fiction, cochlear implants have been on the market since 1982, and more than half a million people are walking around with these bionics in their heads, enjoying voices and door knocks and laughter and piccolos. The software on the cochlear implant is hackable and updateable, so Michael has spent years getting more efficient information through the implant without further surgeries. Almost a year after the implant was activated, he upgraded to a program that gave him twice the resolution. As Michael puts it, “While my friends’ ears will inevitably decline with age, mine will only get better.”
Terry Byland lives near Los Angeles. He was diagnosed with retinitis pigmentosa, a degenerative disorder of his retina, the sheet of photoreceptors at the back of the eye. He reports, “Aged 37, the last thing you want to hear is that you are going blind—that there’s nothing they can do.”2
But then he discovered that there was something he could do, if he was brave enough to try it. In 2004, he became one of the first patients to undergo an experimental procedure: getting implanted with a bionic retinal chip. A tiny device with a grid of electrodes, it plugs into the retina at the back of the eye. A camera on glasses wire-lessly beams its signals to the chip. The electrodes give little zaps of electricity to Terry’s surviving retinal cells, generating signals along the previously silent highway of the optic nerve. After all, Terry’s optic nerve functioned just fine: even while the photoreceptors had died, the nerve remained hungry for signals it could carry to the brain.
A research team at the University of Southern California implanted the miniature chip in Terry’s eye. The surgery was completed without a hitch, and then the real testing began. With hushed anticipation, the research team turned on the electrodes individually to test them. Terry reported, “It was amazing to see something. It was like little specks of light—not even the size of a dime—when they were testing the electrodes one by one.”
Over the course of days, Terry experienced only small constellations of lights: not a rousing success. But his visual cortex gradually figured out how to extract better information out of the signals. After some time, he detected the presence of his eighteen-year-old son: “I was with my son, walking . . . it was the first time I had seen him since he was five years old. I don’t mind saying, there were a few tears wept that day.”
Terry wasn’t experiencing a clear visual picture—it was more like a simple pixelated grid—but the door of darkness had swung open a crack. Over time, his brain has been able to make better sense of the signals. While he can’t ascertain the details of individual faces, he can make them out dimly. And although the resolution of his retinal chip is low, he can touch objects presented at random locations and is able to cross a city street by discerning the white lines of the crosswalk.3 He proudly reports, “When I’m in my home, or another person’s house, I can go into any room and switch the light on, or see the light coming in through the window. When I am walking along the street I can avoid low hanging branches—I can see the edges of the branches, so I can avoid them.”
These digital devices push information that doesn’t quite match the language of the natural biology. Nevertheless, the brain figures out how to make use of the data.
The idea of prostheses for the ear and eye had been seriously considered in the scientific community for decades. But no one was positive that these technologies would work. After all, the inner ear and the retina perform astoundingly sophisticated processing on the sensory input they receive. So would a small electronic chip, speaking the dialect of Silicon Valley instead of the language of our natural biological sense organs, be understood by the rest of the brain? Or instead, would its patterns of miniature electrical sparks come off as gibberish to downstream neural networks? These devices would be like an uncouth traveler to a foreign land who expects that everyone will figure out his language if he just keeps shouting it.
Amazingly, in the case of the brain, such an unrefined strategy works: the rest of the country learns to understand the foreigner.
But how?
The key to understanding this requires diving one level deeper: your three pounds of brain tissue are not directly hearing or seeing any of the world around you. Instead, your brain is locked in a crypt of silence and darkness inside your skull. All it ever sees are electrochemical signals that stream in along different data cables. That’s all it has to work with.
In ways we are still working to understand, the brain is stunningly gifted at taking in these signals and extracting patterns. To those patterns it assigns meaning. With the meaning you have subjective experience. The brain is an organ that converts sparks in the dark into the euphonious