When she did, she became frantic. She ran outside and scanned the street. She couldn’t see him. She went to the neighbors’ house and pounded on the windows. Their homes looked similar-maybe Eugene had become confused and had gone inside? She ran to the door and rang the bell until someone answered. Eugene wasn’t there. She sprinted back to the street, running up the block, screaming Eugene’s name. She was crying. What if he had wandered into traffic? How would he tell anyone where he lived? She had been outside for fifteen minutes already, looking everywhere. She ran home to call the police.
When she burst through the door, she found Eugene in the living room, sitting in front of the television watching the History Channel. Her tears confused him. He didn’t remember leaving, he said, didn’t know where he’d been, and couldn’t understand why she was so upset. Then Beverly saw a pile of pinecones on the table, like the ones she’d seen in a neighbor’s yard down the street. She came closer and looked at Eugene’s hands. His fingers were sticky with sap. That’s when she realized that Eugene had gone for a walk by himself. He had wandered down the street and collected some souvenirs.
And he had found his way home.
Soon, Eugene was going for walks every morning. Beverly tried to stop him, but it was pointless.
“Even if I told him to stay inside, he wouldn’t remember a few minutes later,” she told me. “I followed him a few times to make sure he wouldn’t get lost, but he always came back.” Sometimes he would return with pinecones or rocks. Once he came back with a wallet; another time with a puppy. He never remembered where they came from.
When Squire and his assistants heard about these walks, they started to suspect that something was happening inside Eugene’s head that didn’t have anything to do with his conscious memory. They designed an experiment. One of Squire’s assistants visited the house one day and asked Eugene to draw a map of the block where he lived. He couldn’t do it. How about where his house was located on the street, she asked. He doodled a bit, then forgot the assignment. She asked him to point out which doorway led to the kitchen. Eugene looked around the room. He didn’t know, he said. She asked Eugene what he would do if he were hungry. He stood up, walked into the kitchen, opened a cabinet, and took down a jar of nuts.
Later that week, a visitor joined Eugene on his daily stroll. They walked for about fifteen minutes through the perpetual spring of Southern California, the scent of bougainvillea heavy in the air. Eugene didn’t say much, but he always led the way and seemed to know where he was going. He never asked for directions. As they rounded the corner near his house, the visitor asked Eugene where he lived. “I don’t know, exactly,” he said. Then he walked up his sidewalk, opened his front door, went into the living room, and turned on the television.
It was clear to Squire that Eugene was absorbing new information. But where inside his brain was that information residing? How could someone find a jar of nuts when he couldn’t say where the kitchen was located? Or find his way home when he had no idea which house was his? How, Squire wondered, were new patterns forming inside Eugene’s damaged brain?
II.
Within the building that houses the Brain and Cognitive Sciences department of the Massachusetts Institute of Technology are laboratories that contain what, to the casual observer, look like dollhouse versions of surgical theaters. There are tiny scalpels, small drills, and miniature saws less than a quarter inch wide attached to robotic arms. Even the operating tables are tiny, as if prepared for child-sized surgeons. The rooms are always kept at a chilly sixty degrees because a slight nip in the air steadies researchers’ fingers during delicate procedures. Inside these laboratories, neurologists cut into the skulls of anesthetized rats, implanting tiny sensors that can record the smallest changes inside their brains. When the rats wake, they hardly seem to notice that there are now dozens of microscopic wires arrayed, like neurological spider webs, inside their heads.
These laboratories have become the epicenter for a quiet revolution in the science of habit formation, and the experiments unfolding here explain how Eugene-as well as you, me, and everyone else-developed the behaviors necessary to make it through each day. The rats in these labs have illuminated the complexity that occurs inside our heads whenever we do something as mundane as brush our teeth or back the car out of the driveway. And for Squire, these laboratories helped explain how Eugene managed to learn new habits.
When the MIT researchers started working on habits in the 1990s-at about the same time that Eugene came down with his fever-they were curious about a nub of neurological tissue known as the basal ganglia. If you picture the human brain as an onion, composed of layer upon layer of cells, then the outside layers-those closest to the scalp-are generally the most recent additions from an evolutionary perspective. When you dream up a new invention or laugh at a friend’s joke, it’s the outside parts of your brain at work. That’s where the most complex thinking occurs.
Deeper inside the brain and closer to the brain stem-where the brain meets the spinal column- are older, more primitive structures. They control our automatic behaviors, such as breathing and swallowing, or the startle response we feel when someone leaps out from behind a bush. Toward the center of the skull is a golf ball-sized lump of tissue that is similar to what you might find inside the head of a fish, reptile, or mammal. [16] This is the basal ganglia, an oval of cells that, for years, scientists didn’t understand very well, except for suspicions that it played a role in diseases such as Parkinson’s. [17] [18]
In the early 1990s, the MIT researchers began wondering if the basal ganglia might be integral to habits as well. They noticed that animals with injured basal ganglia suddenly developed problems with tasks such as learning how to run through mazes or remembering how to open food containers. [19] They decided to experiment by employing new micro-technologies that allowed them to observe, in minute detail, what was occurring within the heads of rats as they performed dozens of routines. In surgery, each rat had what looked like a small joystick and dozens of tiny wires inserted into its skull. Afterward, the animal was placed into a T-shaped maze with chocolate at one end.
The maze was structured so that each rat was positioned behind a partition that opened when a loud click sounded. [20] Initially, when a rat heard the click and saw the partition disappear, it would usually wander up and down the center aisle, sniffing in corners and scratching at walls. It appeared to smell the chocolate, but couldn’t figure out how to find it. When it reached the top of the T, it often turned to the right, away from the chocolate, and then wandered left, sometimes pausing for no obvious reason. Eventually, most animals discovered the reward. But there was no discernible pattern in their meanderings. It seemed as if each rat was taking a leisurely, unthinking stroll.
The probes in the rats’ heads, however, told a different story. While each animal wandered through the maze, its brain-and in particular, its basal ganglia-worked furiously. Each time a rat sniffed the air or scratched a wall, its brain exploded with activity, as if analyzing each new scent, sight, and sound. The rat was processing information the entire time it meandered.
The scientists repeated their experiment, again and again, watching how each rat’s brain activity changed as it moved through the same route hundreds of times. A series of shifts slowly emerged. The rats stopped sniffing corners and making wrong turns. Instead, they zipped through the maze faster and faster. And within their brains, something unexpected occurred: As each rat learned how to navigate the maze, its mental activity
It was as if the first few times a rat explored the maze, its brain had to work at full power to make sense of all the new information. But after a few days of running the same route, the rat didn’t need to scratch the walls or smell the air anymore, and so the brain activity associated with scratching and smelling ceased. It didn’t need to choose which direction to turn, and so decision-making centers of the brain went quiet. All it had to do was recall the quickest path to the chocolate. Within a week, even the brain structures related to memory had quieted. The rat had internalized how to sprint through the maze to such a degree that it hardly needed to think at all.
But that internalization-run straight, hang a left, eat the chocolate-relied upon the basal ganglia, the brain probes indicated. This tiny, ancient neurological structure seemed to take over as the rat ran faster and faster and its brain worked less and less. The basal ganglia was central to recalling patterns and acting on them. The basal
