Want To Change Your Habits? You’re Going To Have To Fight Your Brain

Art Markman, PhD, tells us why brainpower is so expensive and how if we want to change behaviors, we need to convince our brains to spend.

Want To Change Your Habits? You’re Going To Have To Fight Your Brain
[Image: Flickr user Jos]

Here is a startling fact: Your brain is designed to spend as little time thinking as possible. That seems like a strange thing to say. After all, any five-year-old can tell you that people think with their brains. And our ability to think, reason, and behave flexibly is truly remarkable. Most people point to our capacity for thought as the factor that truly separates humans from other animals.


The amazing achievements of human beings are a testimony to the tremendous flexibility of the human brain. But that flexibility comes at a cost.

Brains are very expensive to operate. Your brain weighs about three pounds. That means it is 2% to 3% of your body weight. But it takes up a lot of resources. It uses 20% to 25% of the calories you burn each day and requires a lot of oxygen and blood flow to keep it running.

Brains burn through a lot of energy because the active cells in your brain–called neurons–work hard to generate the electrical signals that carry information. Neurons are constantly manufacturing chemicals called neurotransmitters, which help pass signals from one neuron to another. All of this electrical and chemical activity requires a lot of energy to maintain.

Because brains are expensive in terms of energy consumption, most species have fairly small ones. For animals to survive with small brains, the majority of their behaviors are instincts or habits. I got to see this firsthand several years ago, when a baby deer was born in my backyard. I don’t live in the country; Austin, Texas, just has a lot of deer wandering around residential neighborhoods because we have effectively eliminated all of their natural predators. Within minutes, the newborn fawn could stand, and by the end of the day it was walking around. A day later, it had wandered off with its mother.

A deer comes equipped by nature with a variety of complex skills as standard equipment. Because these abilities are wired in, the animals are able to get around with fairly small brains. A typical deer has a brain that weighs about a half pound (which is far less than 1% of its body weight). So compared to people, a deer is not using a tremendous amount of energy to run its brain.

Of course, deer are also not particularly smart or flexible. All of those behaviors that allow a deer to succeed in the forest work less well when confronted with a suburban neighborhood full of cars and houses. A deer spooked by a barking dog will run, even if that dash takes it into the path of oncoming traffic on a busy street. No matter how often a particular deer is nearly hit by cars (and no matter how often they see other deer that are not so lucky), they do not adapt to this environment. Instead, drivers have learn to watch out for the deer.


Humans, of course, are incredibly flexible in their behavior. The first humans lived in a world without modern technology and developed tools from rocks, plants, and animals. Humans of each era, however, are able to learn the technology of the day and to take that cultural complexity as a starting point. This flexibility has two costs, and both involve time.

Unlike the baby deer in my backyard, children do not stand up the day they are born. Or even the day after. It takes months before they can stand up on their own, and months after that to start walking. Most children cannot feed themselves for their first few years of life, and it may take longer before they can prepare their own food. In the modern world, most children don’t even leave home until they are at least 18, and even then they are typically continuing their education. It is common for people to be in their 20s before they are expected to make a contribution to society.

So, clearly, it takes years of programming for humans to develop enough knowledge about their environment to act effectively in the world. Even if the world changes substantially during the course of our lives, we quickly adapt to it. Anyone born before 1970, for example, would have lived years before encountering a computer. Yet most them now use email regularly.

The second cost in time is directly related to this flexibility in behavior. Because you are able to pursue so many different courses of action at any given time, you have to select the behavior you are going to perform, which also takes time.

You cannot afford to spend that much time on all of the things you do. Literally. Benjamin Franklin may have said, “Time is money,” but time is also energy. Your brain wants to minimize the amount of time you spend thinking about anything to make sure the energy cost of thinking does not exceed the value of what you are thinking about.

In any situation, then, your brain has to resolve a trade-off between effort and accuracy. Obviously, you want to do things well. You could run through a new supermarket and throw things into your cart at random. That would certainly get you out of there in a hurry. But you probably wouldn’t get what you need. Then you would have to make another trip, which would waste more time and energy. The trick, then, is to spend exactly as much time as you need to get what you want.


A key way that your brain helps you deal with the trade-off between effort and accuracy is by creating habits. Whenever you do something successful, mechanisms in your brain relate the action you performed to the situation in which you performed it. That way, when the situation comes up again, your brain can suggest that you perform the same action.

As wonderful as habits can be, they’re also one big reason why it’s so hard to change your behavior. Habits develop because the actions you have taken have worked in the past. Your brain wants you to do successful things quickly, so it serves up those behaviors again and again hoping you will be as successful in the future as you were in the past.

If a behavior that worked in the past continues to be successful, your motivational system will continue to promote that habit. If the environment changes, though, and that behavior no longer leads to success, then you generally change that behavior fairly easily.

Suppose that the grocery store decides to reorganize the layout of the wall of tomato sauce. You get to the tomato sauce aisle and notice that it has been organized differently. Perhaps your habit is to look for jars that are at about eye level and slightly to the left. You look there, and the brand you want is not longer in that location. You look around some more and find that now that brand has been moved to a low shelf on the right. You might mistakenly look up and to the left a couple of more times on later shopping trips, but soon you will be looking down and to the right. The old behavior is gone, and the new one replaces it because the old behavior no longer helps you reach your goals.

What really makes behavior change difficult, though, is that sometimes you want to change your behavior even though the old behavior is technically still successful. When you want to diet, for example, your old eating behaviors are still working as far as your motivational system is concerned. You want to eat, and you eat. The problem is that you have some new goals. You may want to lose weight or to feel better. Perhaps your doctor has recommended that you get in shape. So you are now trying to stop satisfying one goal and start satisfying another instead.

In that case, the habits are no longer directing you toward the action you want to take. You have to find a way to stop yourself from doing what you did last time. And that means fighting your brain’s tendency to minimize energy.