Breaking bad habits relies on 'stop' and 'go' brain signals

At the beginning of every new year, a lot of us make resolutions. But by February, many of us have already fallen off the resolution wagon. CBC Radio science columnist Torah Kachur looks at a new study — involving some sugar-happy mice — on why that happens.

Duke University mouse study finds weaker 'go' signal helps break habits

Newly published research from Duke University explores the neurological sources of habitual behaviours like smoking. (Canadian Press)

At the beginning of every new year, a lot of us make resolutions — whether to quit smoking, eat better, or lose weight.

But by February, many of us have already fallen off the resolution wagon. CBC Radio science columnist Torah Kachur looks at a new study from Duke University — involving some sugar-happy mice — on how and why habits are hard to break.

Why is it so hard to break a bad habit?

There are many reasons. Part of what this new study has shown is that habits are wired into our brains. That's why we can perform a habitual behaviour without thinking about it, and why it's so hard to put them under conscious control.

That's not necessarily a bad thing — good habits are an important part of enabling us to do things like operate a car, shower, or brush our teeth, and still have our brains free to focus on other things. That's been an important adaptation for survival.

Habits are programmed into an area of the brain called the basal ganglia — this is quite a complex region of the brain that controls good habits, motor actions, bad habits and compulsive behaviours.

How did the new research explore what's happening in our brains?

The new study, recently published in the journal Neuron, explored the different pathways in the brain that cause habits.

The researchers started by training mice to develop habits. In this case, they trained the mice to press a lever, and in turn the mice received sweets. The animals became hooked on pressing the lever because they were rewarded with a sweet treat.

Duke University neurologist Nicole Calakos was part of the team of researchers whose study focused on the 'stop' and 'go' signals that drive habits. (Duke University/YouTube)
So the researchers decided to look more closely at the brains of the habit-trained mice, compared with untrained mice with no previous sugar habit.

Nicole Calakos is the researcher from Duke University who looked at these mice, and explains what specifically she was looking at in the brain.

"There are two cell types in approximately equal numbers... that more or less have been attributed with giving a 'go' signal to do something, or a 'stop' signal," she said.

So there's the "go" signal — which you could think of as the devil on your shoulder that says, "Go ahead — it's only one cookie. Or four."

And there is a competing pathway in the same area of the brain that is the "stop" signal  —  think of it as the angel on your shoulder that you might call "willpower."

In untrained mice, when they were given the opportunity to press the lever, the "stop" signal came first. In other words, they were better at resisting, and could resist simply because they hadn't formed a habit.

In the trained mice, the default was "go" — their brains told them to press the lever, because they usually do.

What happens in the brain when habits form?

One of the key findings of this study is that there seemed to be a race between the go and stop signals.

Normally, in order to do something that is not habitual, we have to overcome the stop signal with conscious control. We have to tell our bodies to overcome that inhibition.

So there is a switch once you form a habit that enables you to do things without even thinking about it — whether it's a good or bad habit.

What does the new research say about curing bad habits?

It confirms what we intuitively know about our habits. We have to break them by beginning to re-program our brain to say "stop" first.

But the researchers did find something really interesting. The mice that could most easily break the habit had a weaker "go" signal.

So breaking a habit meant reducing the activity of the "go" circuitry, to allow the "stop" signals to be the ones to win the race.

This means for most of us interested in breaking bad habits, we have to consciously stop performing the task for a while so that the "go" signal isn't reinforced, and it weakens with time.

Do the study's results apply to serious addictions?

The study focused on a sugar addiction, but to a certain extent its results apply to other addictions — to nicotine or harder drugs, for example.

The researchers were most interested in simple habits. These do not have or create a chemical dependence in the brain.

When we start talking about drugs like cocaine or nicotine, they have wider effects on the body that a user is also addicted to.

Though the Duke University study focused on mice with a sugar habit, its finding may help people break stronger addictions such as a smoking habit. (iStock)
For instance, nicotine is a vasoconstrictor — meaning it narrows the blood vessels. So it helps you focus and calms you down, in addition to the reward pathway in the brain that it triggers.

So giving up smoking is not as easy as just breaking the habit of performing the act of smoking — you also have to kick the addiction to the drug.

But there certainly are components of addiction that are simply habitual — for example, a smoker might have a coffee and light up a cigarette, even without a big nicotine craving.

Sometimes the solution to that part of the addiction is as simple as doing something with your hands. 

The study is more directly related to compulsive behaviours, and individuals who have detrimental habitual behaviours — those with obsessive-compulsive disorder, Tourette's or autism, for example.

And now that we know significantly more about how the habit forms at the level of the brain circuitry, it will become easier to target those neurons to control the habits.


Torah Kachur

Science Columnist

Torah Kachur has been the syndicated science columnist for CBC Radio One since 2013. Torah received her PhD in molecular genetics from the University of Alberta and studied how worm gonads develop. She now teaches at the University of Alberta as a contract lecturer in cell biology and genetics.


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