National Geographic : 2014 Feb
Seeing the Brain 55 number of neurons carry out a complex task. The function Reid and his colleagues have chosen to decipher is vision. Scientists have been investigating how we see for decades, but they’ve been able to study it only piecemeal. A neuro- scientist might place an electrode in the region of a mouse’s brain involved in visual perception and then note whether nearby neurons fire when the animal sees a particular image. This approach has allowed scientists to map regions of the visual brain that specialize in dif- ferent tasks, such as detecting the edges of an object or perceiving brightness. But scientists haven’t been able to see all those regions work together at once—to learn how the million or so neurons in the visual regions of a mouse’s brain instantly put information together into the image of a cat. Reid and his colleagues are setting out to solve that problem by engineering mice so that their visual neurons will release flashes of light when they fire. The flashes record the neural activity when a mouse sees a specific object, be it a cat, a snake, or an appealing piece of cheese. The scien- tists can then compile the data to create massive mathematical models of vision. If the models are accurate, the researchers will be able to literally read the mind of a mouse. “Our goal is to reconstruct what the mouse sees,” says Reid. “And I think we can do it.” Reid’s research on mouse vision is another step toward neuroscience’s ultimate goal: a com- prehensive view of how this vastly complicated organ really works—what the scientists I talked to call a theory of the brain. Such a grand vision is still a long way off, and for the most part, the search for it has yet to change the way doctors treat patients. But there is one line of research— brain-machine interfaces—where the mapping of the mind has started to change people’s lives. When she was 43 years old, Cathy Hutchin- son suffered a massive stroke, leaving her unable to move or speak. Lying in her bed in Massachu- setts General Hospital, she gradually figured out that her doctors didn’t know if she was brain- dead or still aware. Her sister asked Hutchinson if she could understand her. She managed to answer by moving her eyes up on command. “It gave me such a relief,” Hutchinson tells me 17 years later, “because everybody talked about me as if I was dying.” It is a chilly winter day at her home in eastern Massachusetts, and she’s sitting in a wheelchair in the middle of the living room, dressed in a dark green jogging suit and sneakers. Still almost completely paralyzed and unable to speak, she communicates by looking at letters arrayed on a computer monitor bolted to her wheelchair, a camera tracking the movement of a tiny metal disk attached to the center of her eyeglasses. Near the top of the brain is a region called the motor cortex, where we generate commands to move our muscles. For more than a century we’ve known that each part of the cortex corresponds to a particular area of the body. When people like Hutchinson become paralyzed, the motor cortex often remains intact, but it can’t communicate with the rest of the body, because its connections have been destroyed. John Donoghue, a neuro- scientist at Brown University, wanted to find a way to help people with paralysis by tapping into the signals from their motor cortex. Perhaps they could eventually learn to type on a computer or operate a machine merely with their thoughts. Donoghue spent years developing an implant and testing the device on monkeys. Once he and his colleagues knew it was safe, they were ready to start working with human patients. One of them was Hutchinson. In 2005 sur- geons at Rhode Island Hospital drilled a hole the size of a poker chip in her skull and inserted the sensor for Donoghue’s device. About the size of a ladybug, the sensor contained a hundred min- iature needles, which, pressing into Hutchinson’s motor cortex, recorded the signals from nearby neurons. A set of wires anchored to this device passed through the hole in her skull and led to a metal connector sitting on her scalp. After her surgery had healed, the Brown Uni- versity researchers plugged Hutchinson’s implant into a cable that relayed signal patterns from her brain to a cart of computers they wheeled into her room. As a first step, the scientists trained if their models are accurate, the researchers will be able to literally read the mind of a mouse.