In 1992, an elderly man named Eugene Pauly suddenly forgot who his son was. Then, he started vomiting and ran a fever of 105°F. In the emergency room, he deliriously attacked the nurses. He had viral encephalitis in his brain, which can be extremely dangerous. Fortunately for him, he survived with little damage, though scans showed strange gaps in his brain tissue. Still, within a few weeks, he was walking and talking like normal. But he couldn’t remember almost anything—not the day of the week, his doctor’s name, or who his friends were. Some days he had breakfast several times in a row because he kept forgetting that he’d already eaten.
Cases like Eugene Pauly’s illness are extremely valuable for neuroscience, because they can help researchers determine which parts of the brain contribute to certain abilities and behaviors. Pauly’s infection appears to have affected areas of the brain responsible for memory—but not areas responsible for unconscious abilities like walking and talking. His condition had the potential to help neuroscientists understand the way memories are formed, processed, and stored in the brain. But it also suggests that these memories are very different from the unconscious habits that he still performed.
Eugene Pauly’s wife Beverly brought him to Larry Squire, a memory researcher in San Diego. Squire discovered that while Pauly couldn’t recommend basic information, he could still develop complex habits. Pauly’s brain scans showed that he had lost a small chunk of the middle of his brain. This looked similar to the brain of H.M., a patient who famously lost his memory after brain surgery. But unlike H.M., Eugene could maintain normal conversations and remember his early life. He just couldn’t retain new information for any longer than a minute. He didn’t even know where the rooms in his house were located—yet he could still easily find his way around it. Ultimately, Eugene would revolutionize science’s understanding of habits.
Pauly’s experience strongly suggests that habits depend on different parts of the brain than conscious memory. Somehow, the part of his brain responsible for habits could make use of the new information he learned, but the part responsible for conscious knowledge and decisions couldn’t. This has important implications for people who want to change their habits: they have to alter the right part of the brain. Learning new information can’t lead to forming new habits unless people learn to encode this information in a way that their unconscious, habitual brain can use.
Beverly Pauly started taking Eugene on walks around the block twice a day. One day, he left the house on his own. Frightened that he would get lost, Beverly started frantically looking for him—but she found him back inside the house, watching TV. He had gone on his walk alone and brought back pinecones. He started taking walks every morning, but he could never remember where he had gone. Larry Squire wanted to investigate. He learned that Pauly couldn’t answer basic questions about his neighborhood—but he could guide someone around the neighborhood and back to his home. Clearly, Pauly was learning new information—the question was just how he did it, and where it was located in his brain.
Pauly was able to take walks without consciously remembering or thinking about his route simply because the habit of taking a morning walk doesn’t rely on conscious memory or thought. His condition affirms that habits are fundamentally different from conscious decisions—and it proves that absolutely everyone can change their habits under the right conditions. This meant that Pauly’s life and condition could improve if he learned new habits—even if he didn’t consciously understand what was happening.
At Massachusetts Institute of Technology, there are labs full of miniature surgery tables, where neurologists implant sensors in rats’ brains. The experiments done here are the key to understanding how Eugene Pauly formed new habits. In the 1990s, MIT researchers were studying the basal ganglia, a small, primitive structure at the very center of the brain that seemed important to habit formation. They learned that while rats wandered around a maze looking for chocolate, their brains were highly active—especially their basal ganglia. But when rats repeated the same maze many times, they eventually learned to do it faster, and their brains became less active—except for their basal ganglia, which kept working.
MIT’s research shows that, for the first time, neuroscience is allowing people to understand the hidden, unconscious part of the brain—the part where habits are based. As a rat learned to navigate the maze, its knowledge of this maze gradually moved from the conscious part of its brain (the cortex) to the unconscious part (the basal ganglia). In other words, a specific process may depend on conscious effort at first, but once an organism has repeated it enough, it can learn to do that process unconsciously—turning it into a habit. Of course, this is consistent with the way people learn many skills, ranging from typing to riding a bicycle: at first, they’re difficult and require lots of concentration, but over time, they get easy and become automatic.
The rats learned to navigate the maze through chunking, or “convert[ing] a sequence of actions into an automatic routine.” This is the same process that people use to develop habits, including complex ones like starting a car and backing it out of a driveway. Habits help the brain save effort—which is why the brain tries to turn every routine into a habit if it can. By saving effort, the brain becomes more efficient and can pack more processing power into less space.
Duhigg addresses the key question of why people form habits in the first place. Habits are, in a sense, a kind of technology: they make life easier by automating certain repeatable processes. By developing new habits, people can learn to automate new processes and save themselves energy. In turn, good habits are so valuable because they keep people happy, healthy, and productive without requiring them to expend significant energy.
But saving effort can also be dangerous for the brain, which can miss important cues, like a car speeding into the street behind the driveway. Brain scans show that to compensate for this danger, the brain’s activity spikes right at the beginning and the end of a habit. At the beginning, the brain actively looks for a cue that can tell it which habit to use. Then, the brain powers down during the routine. Finally, at the end of the routine, the brain powers back up to evaluate what happened and receive a reward (whether mental, emotional, or physical). The brain gradually gets used to this three-part loop (cue, routine, reward). Over time, it even learns to expect and crave the reward.
Neuroscientific evidence shows that evolution has programmed the cue-routine-reward habit loop into the human brain to help people conserve energy and make decisions more efficiently. This explains why Duhigg makes this loop so central to his theory of how habits work and change: he wants his readers to use the brain’s built-in machinery to their advantage. In other words, people can consciously trick their unconscious brain into learning new cues, routines, and rewards.
Because the brain diverts its energy elsewhere during a routine, people tend to repeat the same routines automatically—unless they manage to deliberately replace those routines with new ones. While old habits never go away, new ones can still overtake them. Without the basal ganglia, people would be overwhelmed by basic everyday decisions. But the mind’s dependence on habits can also cause problems.
Habits’ energy-saving ability explains both their advantages and disadvantages. On the one hand, habits help people perform complex tasks efficiently and successfully by making them automatic. On the other, habits are also easy to overlook—and often difficult to change—precisely because they are automatic and unconscious. Therefore, people have to make a conscious adjustment if they really want to change their habits.
Eugene Pauly’s basal ganglia were still intact, and Larry Squire wanted to test whether Pauly could still form habits. Squire gave Pauly a memory test over and over again for several weeks. In the test, there were eight pairs of objects; in each pair, one had a sticker saying “correct” on the bottom. Pauly couldn’t remember having done the test before, but after a few weeks, he was choosing almost all of the “correct” objects. But when Squire gave Pauly all sixteen objects and asked him to choose the eight “correct” ones, he couldn’t. This shows that he built a habit loop for the memory test, but he couldn’t actually remember which items were “correct.”
The unconscious part of Pauly’s brain learned to do the memory test, while the conscious part couldn’t. In fact, he couldn’t even remember having done the test before. Since habit is largely unconscious, people are often as unaware of their own habits, as Pauly was of his. This underlines the counterintuitive fact that conscious memory and habit are totally separate processes. Learning new habits requires bridging this gap—using the conscious part of the brain to teach the unconscious part new tricks.
Eugene Pauly could also form other habits—like his daily walks. He could also act out his anger, even when he couldn’t remember why he was angry. But when his cues subtly shifted, his habits stopped working. For instance, when there was construction in his neighborhood, he couldn’t find his way home on his walks. By studying Pauly, Larry Squire proved that people can unconsciously learn things and make decisions without remembering or understanding them.
Pauly lost his habits due to shifting cues, which shows how delicate the habit loop is: cues, routines, and rewards have to stay exactly the same over time in order for the loop to continue functioning. This makes it relatively easy to break good habits, but also to modify bad ones. Thus, the key to controlling one’s habits is carefully controlling these cues, routines, and rewards.
In the decades since Larry Squire published his research on Eugene Pauly, hundreds of scientists all around the world have started to study habits. Habits can involve all sorts of cues, routines, and rewards. They are “powerful, but delicate”—people can build and alter them either consciously or unintentionally, and they can often override common sense. For instance, scientists have shown that mice will continue pushing a lever to receive food even when they know the food is poisonous. This is similar to why many people frequently eat fast food, despite their intentions to avoid it. In fact, McDonald’s designs its restaurants and food to give customers consistent cues and immediate rewards.
Duhigg started his book with Eugene Pauly because Squire’s research on him is the foundation of contemporary scientific studies on habit. These studies have helped explain many of the common-sense mysteries about habit—like why people struggle to overcome habits that they know are bad for them. As Duhigg explains here, this tendency happens because the habit loop occurs in the primitive, unconscious part of the brain. Therefore, it continues automatically, even when people consciously want to stop their habits. In other words, the brain doesn’t distinguish between good and bad habits on its own. Meanwhile, corporations like McDonald’s manipulate people into adopting bad habits by using the same research that Duhigg hopes his readers can use to break those bad habits.
Over time, Eugene Pauly settled into new habits. He went on walks, ate what he wanted, and spent most of his time watching the History Channel. But these habits became dangerous—he spent too long in front of the TV, didn’t stay on a healthy diet, and couldn’t remember to be careful on his walks as he aged. Beverly helped improved his diet, but it wasn’t enough to improve his health.
Pauly’s life shows both the positive and negative sides of habits. On the one hand, because habits are so powerful, he was able to enjoy a reasonable quality of life by learning and repeating new habits. On the other, because habits are automatic, he ended up repeating the same behaviors to an extreme and put his own health in danger.
When Eugene Pauly had a heart attack, he kept ripping off his chest monitors in the hospital. His daughter convinced him to keep them on by having the nurses repeatedly compliment him for sitting still. Later, he broke his hip, and after settling comfortably into the hospital for a few weeks, he died of a heart attack. He made a profound contribution to science, even if he never fully remembered it.
Just as McDonald’s exploits the habit loop to make people eat unhealthy food, Pauly’s daughter used cues, routines, and rewards to get him to keep his chest monitors on (and possibly save his life). Again, this shows that habits and habit modification are a tool—they can be used for good or evil, depending on who implements them and in what context they do so.