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I鈥橫 STARING down at my fingers on the keyboard with some shame and disappointment. I expected them to look different by now. When I set out to write about habits, I vowed to break one of my own 鈥� biting my nails. The gnawed tips remind me what everyone knows: old habits die hard.

Just why habits are so hard to make and break is a long-standing mystery. Even so, the prospect of mastering our habits has such appeal that plenty of theories about them have evolved. Accepted wisdom suggests, for instance, that it takes 21 days to form a new habit or get rid of an old one.

Unfortunately, there鈥檚 little by way of evidence to back up such notions. But that is starting to change. With advances in neuroscience, it is now possible to peer inside the brain as it goes about its business, which means for the first time we are building an accurate picture of just what happens to brain circuitry when a new habit is formed. We鈥檝e even figured out ways to switch habits on and off with the flick of a switch.

The first challenge in understanding habits is getting to grips with what one actually is. In the vernacular, we might refer to habits as anything from brushing our teeth to bad table manners or smoking.

Scientifically, habits are defined fairly broadly as actions performed routinely in certain contexts and situations, often unconsciously. Once a habit is formed, you might think of it like initiating a program that runs on autopilot, making our actions more streamlined.

鈥淔orty per cent of our daily behaviour is habitual, freeing up the mind鈥�

This process plays a vital part in making our everyday lives easier: imagine if you had to give your full attention to brushing your teeth or the commute to work every time you did it 鈥� life would become exhausting. 鈥淪o much of our lives actually wind up being our habitual behaviours, that alone is amazing,鈥� says , a neuroscientist at the Massachusetts Institute of Technology. In fact, as much as , according to , now at the University of Southern California, who tracked student behaviour to see how much of it fell into this kind of mental autopilot. She found that when students were engaged in well-practised behaviours 鈥� such as driving, exercising or brushing their teeth 鈥� they were often thinking of something else, allowing them to ruminate and their mind to wander.

All this makes sense from a practical perspective, but it also suggests that something changes in the brain when a conscious action turns into a habit.

This is one of the questions Graybiel is studying in her lab. Much of her work involves monitoring the brain activity of rodents and primates as they learn new activities and then repeat them until they eventually become habitual.

One of the first things her lab discovered was to do with an area of the brain called the striatum, a region important for movement, mood and reward. After a rat learns to navigate a maze and begins to follow the same route out of habit, brainwaves slow down in this part of the brain. Graybiel suspects that this slowing down indicates the creation of the habit, probably because the brain activity in that region has .

In another study, when monkeys were rewarded after looking at a series of dots, they soon learned the optimal strategy 鈥� the quickest way to look at every dot and get a juice reward the fastest. Again, after a certain point, the firing of the cells in as the monkeys鈥� behaviour shifted to habit.

Importantly, the studies showed that cells within the striatum fire in this way at the beginning and end of a behaviour, as if signalling when the autopilot program is turned on and off. Graybiel has seen this time and again in her studies of rats and monkeys. 鈥淏y the time they really learned the habit, a lot of the neuronal activity had moved over to occurring at the beginning and the end of the whole behaviour, as though to package it, to mark the onset and offset of behaviour,鈥� she says. You might think of this as the brain鈥檚 equivalent of putting the habitual action between brackets. Graybiel calls it 鈥渃hunking鈥�, as a homage to psychologist George Miller鈥檚 ideas about how it鈥檚 easier to remember lists of things if you 鈥渃hunk鈥� them together into discrete blocks. If you were interrupted while reciting a phone number, says Graybiel, you鈥檇 probably have to start over, because you only know it as a full thing.

This chunking of habits is what allows us to avoid wasting valuable brain power on simple activities. But it also has a downside: it makes breaking bad habits incredibly difficult.

The problem comes from assuming that we are always goal-directed, motivated people when we actually don鈥檛 have conscious access to our habits, says David Neal, founder of Catalyst Behavioral Sciences, a consulting firm specialising in understanding consumers鈥� decision-making and habits. For instance, I think I bite my nails to relieve stress, and can stop if I want to; in truth, I bite my nails without realising it. Simply wanting to stop isn鈥檛 enough, because habits are unconscious impulses, firmly wired into our brains.

Understanding this could contribute in other ways though. The striatum helps to chunk habits, but Graybiel also suspects the involvement of a small brain area called the infralimbic cortex. Previous studies found that when animals had this brain area removed, they either abandoned their habits or acted in more goal-directed ways.

Because neurons within the infralimbic cortex change their firing pattern as habits are formed and broken, Graybiel decided to target the region with optogenetics, a precise technique that allows neurons to be turned on and off with flashes of light. When the region was deactivated, the habit was immediately disrupted; the rats no longer followed their usual route. With time, the rats formed a new habit of running in the other direction, until Graybiel thwarted them again with another flash to their infralimbic cortex. When she did, .

鈥淲illpower comes in limited supply, and gets used up during the day鈥�

This raises the intriguing possibility that targeting this area could help us break bad habits (see 鈥�Pathological habits?鈥�). But optogenetics hasn鈥檛 been tried on the human brain yet. Transcranial magnetic stimulation 鈥� which applies small electrical currents to the outside of the head 鈥� is one alternative, and it is already being studied for treating addiction. Deep brain stimulation 鈥� in which an implanted electrode is used to activate a certain brain region 鈥� is another option. It is currently used to treat depression and Parkinson鈥檚 disease. Studies on obsessive-compulsive disorder, which is associated with very persistent behaviours, have been mixed.

Still, right now, that doesn鈥檛 help my nail biting habit, or another aspect of habit that I was especially curious about. I wanted to know: does the brain distinguish between habits that we want to keep and ones we are trying to ditch? And so, as I wanted to stop taking things like the ability to run for granted, I resolved to keep a gratitude journal every day.

Some evidence about how the brain processes good and bad habits comes from another of Graybiel鈥檚 experiments 鈥� a set-up that mimicked bad ones. Rats learned to navigate a simple maze 鈥� turn left for chocolate milk, say 鈥� until running this route was engrained. When given chocolate milk laced with a chemical that made them sick, the rats still ran the same route, despite having no desire for chocolate milk anymore. They couldn鈥檛 help it 鈥� it was habitual.

Studies of willpower also build on the idea that the brain doesn鈥檛 discriminate between good and bad habits. Willpower, it seems, comes in limited supply; the more we use it during the day 鈥� to resist the office doughnuts, to go the gym when we鈥檇 rather not 鈥� the more it gets depleted, which means we鈥檙e more likely to give up on later attempts.

Fortunately, our reserves are restored overnight, so we start with a fresh supply each day, says Richard O鈥機onnor, a psychotherapist and author of the book . But when it is in short supply 鈥� in times of stress or exhaustion, for example 鈥� we fall back on our habits, whether good or bad. As my deadlines get closer, my nails get shorter. And it鈥檚 perhaps not surprising that . But good habits, like reading more or exercising, also increase.

This is because there are two competing systems in the brain, says Neal, who studied the students during exam weeks: a goal-directed system and a habit-forming one. 鈥淭he goal-directed system is expensive to run; it takes effort and lots of mental resources.鈥� When it gets tied up, as during a week of exhausting exams, the habit system kicks in. But, he says, 鈥渢he habit system has both good things in it and bad things in it. So you get kind of a boost across the board.鈥�

鈥淧eople fall back on whatever habits are strongest,鈥� says Wood. She recently conducted a study in which people who had been trained to eat healthy foods ate less chocolate even when their willpower was low. Chocoholics, on the other hand, .

What makes one habit stronger than another? Most habits start off as goal-directed behaviours: you want a cleaner bedroom, so you make your bed each morning; I wanted to be more grateful, so I started a journal. But if done often enough, they become automatic, performed unconsciously. And this switch between the two can also be seen in the brain.

, now at the University of California, San Diego, taught mice to press a lever for a sugary drink in either a goal-directed way (only when they were hungry) or a habitual manner (every time they entered a particular room).

Next, Gremel used optogenetics and chemical methods to disrupt certain brain areas. When a region called the orbitofrontal cortex was inhibited, the animals started acting more habitually, pressing for food even when full. And when the area was activated, .

鈥淭here are individual differences in how the brain is wired for habits鈥�

Gremel has distinguished between the different parts of the brain responsible for both systems in mice: goal-directed behaviours rely on the orbitofrontal cortex and a medial part of the striatum (which is analogous to a region called the caudate in humans) while habits rely on a lateral part of the striatum (the putamen in humans).

The results hold up in experiments on people too. at the University of Amsterdam in the Netherlands examined differences in how often people make 鈥渟lips of action鈥�, falling back on habits when they don鈥檛 intend to, like driving towards work when they meant to drive to the grocery store. In the study, people learned to play a computer game for a monetary reward. Then the rules of the game were changed. Those who were more prone to slips of action would continue to hit the buttons they were used to, even if it lost them money. When their brains were scanned, these people had stronger connections between the putamen and cortex compared with people who were better able to remain goal directed (to adjust to the new rules and keep earning money). The between the caudate and cortex.

So there are individual differences in how our brains are wired for habits. To some, the key to making and breaking habits is understanding these differences.鈥漎ou look at all the advice we鈥檙e surrounded by: do it first thing in the morning, start small, give yourself a cheat day鈥� They all work sometimes for some people, but they don鈥檛 work all the time,鈥� says , author of Better Than Before: Mastering the habits of our everyday lives.

O鈥機onnor agrees: in his book, he identifies factors that may lead to bad habits: a tendency towards excessive risk-taking or perfectionism, for example. Like Rubin, he stresses that the first step to better habits is gaining self-knowledge and insight into your personality, triggers and ingrained responses.

We also know that habits are triggered by certain cues or contexts. Indeed, it could be these cues that kick off brain signals that tell the striatum to 鈥渙pen brackets鈥� and begin that autonomous behaviour. We are driven to do certain things in certain environments. Neal and Wood studied this by having people watch videos in a cinema or a conference room. In both settings, the participants were given either freshly popped popcorn or week-old popcorn. People who were used to eating popcorn at the cinema ate more of the stale popcorn in that setting, even when they admitted it wasn鈥檛 very good. But in the conference room, they didn鈥檛 eat as much. .

So the next step is coming up with a well-defined plan based on such cues. I wanted to write in my journal at the end of each day, so I put it next to my bed. Before I turned out the light, I鈥檇 write.

鈥淧eople who form such simple concrete plans are generally much more effective,鈥� says de Wit. Having specific rules also makes it easier to make good choices, even when your willpower is low.

Clean break

The link between habits and our environment is also why the best times to break habits or create new ones are when we go on a trip, change jobs or move house. Wood studied students鈥� habits before and after transferring university and found that like how much they watched television or went to the gym, for better or worse. The context got disrupted, allowing new habits to form.

And even small changes to routine can help 鈥� like the cue to put my diary by my bed. 鈥淭hose little disruptions to the environment actually make a big difference. It鈥檚 surprising,鈥� says Neal.

For my nail-biting, working out a way to break the cue was harder: I needed my fingers to type. Neal suggested painting my nails, to disrupt the sensory experience. It worked, for a bit.

But after about a week of painted nails, the polish chipped and I removed it. I promised to repaint them soon, but, before I even realised it, I had bitten them down again.

Another tip is not to worry about little slip-ups like this. A University College London study that followed about 100 people as they tried to form new habits found no long-term consequences to slipping up for a day here or there. So if you diet for a month, but then fall off for a day, don鈥檛 take that to mean you鈥檝e failed. 鈥淵ou got 30 days of dieting practice built up in your brain,鈥� says O鈥機onnor. 鈥淭hat doesn鈥檛 go away just because you slipped up on day 31.鈥� To prevent slip-ups from snowballing, Rubin suggests breaking the day into sections. That way, if you eat too many doughnuts at a morning meeting, you don鈥檛 give up and binge for the rest of the day. Rather, you start fresh at noon and try again.

And it gets easier, O鈥機onnor promises. 鈥淲hatever you do, you鈥檙e more likely to do it again because you鈥檝e just done it.鈥� Willpower is like a muscle; although it can get depleted, it also gets stronger with practice.

How long do you need to practise for? O鈥機onnor says to give it at least three months, which is longer than the often-repeated mantra that it takes 21 days for habits to form. The University College London study found that there was huge variation in how long it took to cement a new habit. , but it ranged between 18 and 254.

My experience backs this up. My journalling habit came easily; within a week or two, it was second nature. Stopping the nail biting, however, seems to be on the 254-day pace, if that. But knowing that it can take months means I鈥檓 persevering. Besides, I鈥檝e realised it can be hard for everyone. Even de Wit admits being unable to stop popping her bubble gum, to the chagrin of her partner. 鈥淯nfortunately, when you study habits it doesn鈥檛 mean you don鈥檛 have any bad habits,鈥� she says. Writing about them doesn鈥檛 guarantee it, either.

(Images: Artwork: Stephan Schmitz; Corey Hendrickson / Aurora Photos; Pablo del rio sotelo/Getty; Yujiro Tada/Getty)

This article appeared in print under the headline 鈥淔orce of habit鈥�

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