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Rats, Monkeys, and other Nail-Biting Stuff

The Power of Habit: Why We Do What We Do in Life and Business is a book written in 2012 by Pulitzer-prize winning American journalist Charles Duhigg. It explores the science behind how habits are created as well as reformed in human beings.

The author splits his book into three sections. First, he talks about the habits of individuals, and then the habits of successful organisations, and finally the habits of societies. This article is not a review of the book, rather it is an attempt to summarise the first section i.e. the habits of individuals.

What is a Habit? 

The author tells us that a habit can be described using a loop which has three components, the Cue, the Routine, and the Reward. He explains this through an experiment done in the Massachusetts Institute of Technology. In this experiment, some rats were wired up with probes in their brains and then placed behind a screen. When each rat heard a loud click, the screen would lift, and it would enter a maze where it had to find the chocolate which was hidden somewhere inside.

In the beginning, each rat moved randomly and took ages getting to the chocolate. But the more times the experiment was repeated – with the chocolate in the same place – the quicker the rats reached their goal.

The brain scans of these rats revealed something interesting. The brain activity for each rat was extremely high the first time it entered the maze. But the more times the rat entered the maze, its brain activity decreased. Soon the rat could reach the chocolate without utilising the decision-making centres or even the memory centres of the brain. It would sprint towards the chocolate hardly needing to think at all.

The brain had turned a group of actions (which require a lot of brain activity) into an automatic routine (which requires very little brain activity). This is essentially how habits are formed. The brain is constantly looking for ways to conserve energy. It stores useful information as routines such that the body can carry out these routines even while the brain is dormant.

But it’s not always useful for us to be doing actions while our brains are dormant. In fact, we often need our brains to be alert. So how does the brain decide when to go into autopilot mode? This is where the Cue comes in. The Cue tells the brain that it is now time to implement an automatic Routine. For the rats, the Cue was the loud click they heard as the screen was lifted. Once the brain had registered the Cue, it could implement the Routine, which was to run through the maze using a certain path until it reached the chocolate, which was the Reward. The Reward is important as it tells the brain that this Cue and Routine is worth remembering for the future.   

The Secret Ingredient

If we look the rat experiment, we find that it’s nothing but basic learning. So how did this learning turn into a habit? The author explains this using an experiment done in the University of Cambridge, this time on monkeys. Again, the monkeys’ brains were wired up and they were put in front of a computer screen. Every time a particular shape came up on the screen, the monkey had to press a button in front of it. And as a reward, it would receive a drop of fruit juice from a tube hanging from the ceiling.

It took a while for the monkeys to get the hang of it, but soon they were pressing the button whenever the correct shape came up on the screen, and they would get a drop of fruit juice. Each time they got the fruit juice, there would be a spike in brain activity indicating the reward. Gradually this activity became a habit, with the Cue being the shape on the screen, the Routine being pushing the button, and the Reward being the fruit juice.

However, as the experiment progressed, and the habit became stronger, a change in the brain was revealed. In the beginning, there was a spike in brain activity after the monkey had tasted the juice. But now, the spike in brain activity was happening as soon the shape came up on the screen, before the juice was even given. The monkeys were now anticipating the Reward.

The scientists then adjusted the experiment. When the monkeys pushed the buttons correctly, the juice would arrive late, or it would arrive diluted, or it wouldn’t arrive at all. At this, the monkeys would get angry. The spike in brain activity relating to the receiving of the Reward had already happened, but they did not end up receiving the actual Reward. This created a new activity in the brain; craving.

The scientists then opened the door so the monkeys could leave. For some monkeys, who hadn’t been playing the game for long, the distraction was enough, and they would leave. But for others, the craving had become so strong, no distraction could make them stop playing the game. This explains why habits are so powerful. They create cravings. And it is this Craving which powers the habit loop. 

For example, in a smoker, the Cue could be the feeling of being stressed, the Routine could be smoking a cigarette, and the Reward would be the feeling of being relaxed. But the Craving is for the nicotine. The loop isn’t enough to sustain a habit on its own. There has to be a Craving.

Creating a New Habit

So now armed with all this information, how does one go about creating a new habit? Let’s say you want to start a habit of going for a jog every morning. Well you’ll need to begin with a Cue. Perhaps you’ll leave your running clothes besides your bed the night before. And when you wake up, you’ll see it and take it as your Cue to start your Routine. Your Routine would obviously be to go for a run. And then you’d give yourself a Reward. Perhaps a delicious smoothie or something. But also remember, to keep this a consistent habit, there needs to be a Craving. Your Craving could be an endorphin rush you get from doing exercise or maybe it could be just a sense of accomplishment you get from completing a strenuous task.

Getting Rid of a Bad Habit

Here the author introduces what he calls the Golden Rule. And this is, “You cannot extinguish a bad habit, you can only change it.” This means you keep the Cue and Reward the same, and only change the Routine based upon what the Craving is.

He explains this using the example of a young student who had a habit of biting her nails all the time. This habit had gotten so bad that her fingers would often bleed, and her fingertips were permanently covered with scabs. She was referred to a therapist who tried to figure out her habit loop. He first found her Cue. She would run her thumb across her fingernails and notice rough edges. Then her Routine would be to bite all her nails until she thinks they’ve smoothened. And her Reward would be “a brief sense of completeness.” But what was her craving? After talking it through, it soon became clear that she only bit her nails when she was bored. She was craving physical stimulation.

To change the habit, a new loop was required. The therapist kept the student’s Cue and Reward the same. But he had to change her Routine. Every time she did her Cue and felt the urge to bite her nails, he told her to note it down and then quickly do something that would physically prevent her from doing the Routine e.g. sitting on her hands or shoving them into her pockets. And then he told her to do something such as rubbing her arm or tapping the table as this would provide the physical stimulation she was craving

The student went back to the therapist after a week. She had only bitten her nails three times.  And after a month, she wasn’t biting her nails at all. Due to this new loop, a new habit had formed, and an old habit of a lifetime had been destroyed. 


Habits are extremely powerful. They often occur without our permission and shape a large part of our lives. Once we know how habits emerge and how they can be changed, we now have the responsibility to break them down and rebuild them to our own specifications. Rather than let our habits govern us, we must transform them so they can be utilised to achieve our goals.

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