THE HABIT LOOP
How Habits Work
In the fall of 1993, a man who would upend much of what we know about
habits walked into a laboratory in San Diego for a scheduled
appointment. He was elderly, a shade over six feet tall, and neatly
dressed in a blue button-down shirt. His thick white hair would have
inspired envy at any fiftieth high school reunion. Arthritis caused him
to limp slightly as he paced the laboratory's hallways, and he held his
wife's hand, walking slowly, as if unsure about what each new step would
About a year earlier, Eugene Pauly, or "E.P." as he would come to be
known in medical literature, had been at home in Playa del Rey,
preparing for dinner, when his wife mentioned that their son, Michael,
was coming over.
"Who's Michael?" Eugene asked.
"Your child," said his wife, Beverly. "You know, the one we raised?"
Eugene looked at her blankly. "Who is that?" he asked.
The next day, Eugene started vomiting and writhing with stomach cramps.
Within twenty-four hours, his dehydration was so pronounced that a
panicked Beverly took him to the emergency room. His temperature started
rising, hitting 105 degrees as he sweated a yellow halo of perspiration
onto the hospital's sheets. He became delirious, then violent, yelling
and pushing when nurses tried to insert an IV into his arm. Only after
sedation was a physician able to slide a long needle between two
vertebra in the small of his back and extract a few drops of
The doctor performing the procedure sensed trouble immediately. The
fluid surrounding the brain and spinal nerves is a barrier against
infection and injury. In healthy individuals, it is clear and quick
flowing, moving with an almost silky rush through a needle. The sample
from Eugene's spine was cloudy and dripped out sluggishly, as if filled
with microscopic grit. When the results came back from the laboratory,
Eugene's physicians learned why he was ill: He was suffering from viral
encephalitis, a relatively common disease that produces cold sores,
fever blisters, and mild infections on the skin. In rare cases, however,
the virus can make its way into the brain, inflicting catastrophic
damage as it chews through the delicate folds of tissue where our
thoughts, dreams-and according to some, souls- reside.
Eugene's doctors told Beverly there was nothing they could do to counter
the damage already done, but a large dose of antiviral drugs might
prevent it from spreading. Eugene slipped into a coma and for ten days
was close to death. Gradually, as the drugs fought the disease, his
fever receded and the virus disappeared. When he finally awoke, he was
weak and disoriented and couldn't swallow properly. He couldn't form
sentences and would sometimes gasp, as if he had momentarily forgotten
how to breathe. But he was alive.
Eventually, Eugene was well enough for a battery of tests. The doctors
were amazed to find that his body-including his nervous system- appeared
largely unscathed. He could move his limbs and was responsive to noise
and light. Scans of his head, though, revealed ominous shadows near the
center of his brain. The virus had destroyed an oval of tissue close to
where his cranium and spinal column met. "He might not be the person you
remember," one doctor warned Beverly. "You need to be ready if your
husband is gone."
Eugene was moved to a different wing of the hospital. Within a week, he
was swallowing easily. Another week, and he started talking normally,
asking for Jell-O and salt, flipping through television channels and
complaining about boring soap operas. By the time he was discharged to a
rehabilitation center five weeks later, Eugene was walking down hallways
and offering nurses unsolicited advice about their weekend plans.
"I don't think I've ever seen anyone come back like this," a doctor told
Beverly. "I don't want to raise your hopes, but this is amazing."
Beverly, however, remained concerned. In the rehab hospital it became
clear that the disease had changed her husband in unsettling ways.
Eugene couldn't remember which day of the week it was, for instance, or
the names of his doctors and nurses, no matter how many times they
introduced themselves. "Why do they keep asking me all these questions?"
he asked Beverly one day after a physician left his room. When he
finally returned home, things got even stranger. Eugene didn't seem to
remember their friends. He had trouble following conversations. Some
mornings, he would get out of bed, walk into the kitchen, cook himself
bacon and eggs, then climb back under the covers and turn on the radio.
Forty minutes later, he would do the same thing: get up, cook bacon and
eggs, climb back into bed, and fiddle with the radio. Then he would do
Alarmed, Beverly reached out to specialists, including a researcher at
the University of California, San Diego, who specialized in memory loss.
Which is how, on a sunny fall day, Beverly and Eugene found themselves
in a nondescript building on the university's campus, holding hands as
they walked slowly down a hallway. They were shown into a small exam
room. Eugene began chatting with a young woman who was using a computer.
"Having been in electronics over the years, I'm amazed at all this," he
said, gesturing at the machine she was typing on. "When I was younger,
that thing would have been in a couple of six-foot racks and taken up
this whole room."
The woman continued pecking at the keyboard. Eugene chuckled.
"That is incredible," he said. "All those printed circuits and diodes
and triodes. When I was in electronics, there would have been a couple
of six-foot racks holding that thing."
A scientist entered the room and introduced himself. He asked Eugene how
old he was.
"Oh, let's see, fifty-nine or sixty?" Eugene replied. He was seventy-
one years old.
The scientist started typing on the computer. Eugene smiled and pointed
at it. "That is really something," he said. "You know, when I was in
electronics there would have been a couple of six-foot racks holding
The scientist was fifty-two-year-old Larry Squire, a professor who had
spent the past three decades studying the neuroanatomy of memory. His
specialty was exploring how the brain stores events. His work with
Eugene, however, would soon open a new world to him and hundreds of
other researchers who have reshaped our understanding of how habits
function. Squire's studies would show that even someone who can't
remember his own age or almost anything else can develop habits that
seem inconceivably complex-until you realize that everyone relies on
similar neurological processes every day. His and others' research would
help reveal the subconscious mechanisms that impact the countless
choices that seem as if they're the products of well- reasoned thought,
but actually are influenced by urges most of us barely recognize or
By the time Squire met Eugene, he had already been studying images of
his brain for weeks. The scans indicated that almost all the damage
within Eugene's skull was limited to a five-centimeter area near the
center of his head. The virus had almost entirely destroyed his medial
temporal lobe, a sliver of cells which scientists suspected was
responsible for all sorts of cognitive tasks such as recall of the past
and the regulation of some emotions. The completeness of the destruction
didn't surprise Squire-viral encephalitis consumes tissue with a
ruthless, almost surgical, precision. What shocked him was how familiar
the images seemed.
Thirty years earlier, as a PhD student at MIT, Squire had worked
alongside a group studying a man known as "H.M.," one of the most famous
patients in medical history. When H.M.-his real name was Henry Molaison,
but scientists shrouded his identity throughout his life-was seven years
old, he was hit by a bicycle and landed hard on his head. Soon
afterward, he developed seizures and started blacking out. At sixteen,
he had his first grand mal seizure, the kind that affects the entire
brain; soon, he was losing consciousness up to ten times a day.
By the time he turned twenty-seven, H.M. was desperate. Anticonvulsive
drugs hadn't helped. He was smart, but couldn't hold a job. He still
lived with his parents. H.M. wanted a normal existence. So he sought
help from a physician whose tolerance for experimentation outweighed his
fear of malpractice. Studies had suggested that an area of the brain
called the hippocampus might play a role in seizures. When the doctor
proposed cutting into H.M.'s head, lifting up the front portion of his
brain, and, with a small straw, sucking out the hippocampus and some
surrounding tissue from the interior of his skull, H.M. gave his
The surgery occurred in 1953, and as H.M. healed, his seizures slowed.
Almost immediately, however, it became clear that his brain had been
radically altered. H.M. knew his name and that his mother was from
Ireland. He could remember the 1929 stock market crash and news reports
about the invasion of Normandy. But almost everything that came
afterward-all the memories, experiences, and struggles from most of the
decade before his surgery-had been erased. When a doctor began testing
H.M.'s memory by showing him playing cards and lists of numbers, he
discovered that H.M. couldn't retain any new information for more than
twenty seconds or so.
From the day of his surgery until his death in 2008, every person H.M.
met, every song he heard, every room he entered, was a completely fresh
experience. His brain was frozen in time. Each day, he was befuddled by
the fact that someone could change the television channel by pointing a
black rectangle of plastic at the screen. He introduced himself to his
doctors and nurses over and over, dozens of times each day.
"I loved learning about H.M., because memory seemed like such a
tangible, exciting way to study the brain," Squire told me. "I grew up
in Ohio, and I can remember, in first grade, my teacher handing everyone
crayons, and I started mixing all the colors together to see if it would
make black. Why have I kept that memory, but I can't remember what my
teacher looked like? Why does my brain decide that one memory is more
important than another?"
When Squire received the images of Eugene's brain, he marveled at how
similar it seemed to H.M.'s. There were empty, walnut-sized chunks in
the middle of both their heads. Eugene's memory-just like H.M.'s-had
As Squire began examining Eugene, though, he saw that this patient was
different from H.M. in some profound ways. Whereas almost everyone knew
within minutes of meeting H.M. that something was amiss, Eugene could
carry on conversations and perform tasks that wouldn't alert a casual
observer that anything was wrong. The effects of H.M.'s surgery had been
so debilitating that he was institutionalized for the remainder of his
life. Eugene, on the other hand, lived at home with his wife. H.M.
couldn't really carry on conversations. Eugene, in contrast, had an
amazing knack for guiding almost any discussion to a topic he was
comfortable talking about at length, such as satellites- he had worked
as a technician for an aerospace company-or the weather.
Squire started his exam of Eugene by asking him about his youth. Eugene
talked about the town where he had grown up in central California, his
time in the merchant marines, a trip he had taken to Australia as a
young man. He could remember most of the events in his life that had
occurred prior to about 1960. When Squire asked about later decades,
Eugene politely changed the topic and said he had trouble recollecting
some recent events.
Squire conducted a few intelligence tests and found that Eugene's
intellect was still sharp for a man who couldn't remember the last three
decades. What's more, Eugene still had all the habits he had formed in
his youth, so whenever Squire gave him a cup of water or complimented
him on a particularly detailed answer, Eugene would thank him and offer
a compliment in return. Whenever someone entered the room, Eugene would
introduce himself and ask about their day.
But when Squire asked Eugene to memorize a string of numbers or describe
the hallway outside the laboratory's door, the doctor found his patient
couldn't retain any new information for more than a minute or so. When
someone showed Eugene photos of his grandchildren, he had no idea who
they were. When Squire asked if he remembered getting sick, Eugene said
he had no recollection of his illness or the hospital stay. In fact,
Eugene almost never recalled that he was suffering from amnesia. His
mental image of himself didn't include memory loss, and since he
couldn't remember the injury, he couldn't conceive of anything being
In the months after meeting Eugene, Squire conducted experiments that
tested the limits of his memory. By then, Eugene and Beverly had moved
from Playa del Rey to San Diego to be closer to their daughter, and
Squire often visited their home for his exams. One day, Squire asked
Eugene to sketch a layout of his house. Eugene couldn't draw a
rudimentary map showing where the kitchen or bedroom was located. "When
you get out of bed in the morning, how do you leave your room?" Squire
"You know," Eugene said, "I'm not really sure."
Squire took notes on his laptop, and as the scientist typed, Eugene
became distracted. He glanced across the room and then stood up, walked
into a hallway, and opened the door to the bathroom. A few minutes
later, the toilet flushed, the faucet ran, and Eugene, wiping his hands
on his pants, walked back into the living room and sat down again in his
chair next to Squire. He waited patiently for the next question.
At the time, no one wondered how a man who couldn't draw a map of his
home was able to find the bathroom without hesitation. But that
question, and others like it, would eventually lead to a trail of
discoveries that has transformed our understanding of habits' power. It
would help spark a scientific revolution that today involves hundreds of
researchers who are learning, for the first time, to understand all the
habits that influence our lives.
As Eugene sat at the table, he looked at Squire's laptop.
"That's amazing," he said, gesturing at the computer. "You know, when I
was in electronics, there would have been a couple of six-foot racks
holding that thing."
Excerpted from "The Power of Habit: Why We Do What We Do in Life and Business" by Charles Duhigg. Copyright © 0 by Charles Duhigg. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher. Excerpts are provided solely for the personal use of visitors to this web site.