Blame Your Bad Habits on Your Brain

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If you struggle to break a bad habit, new research published in the journal Neuron suggests that adaptive brain circuitry may be more responsible than faulty willpower. Researchers at Duke University found that habit-forming behaviors have a specific neural signature in the basal ganglia, the part of your brain involved in controlling motor actions and implicated in compulsive behaviors like OCD and addiction.

The team, headed by Nicole Calakos, an associate professor of neurology and neurobiology at Duke University Medical Center, set out to study whether there they could find specific neurons involved in compulsive behaviors in the brains of mice. They began with the hypothesis that certain behaviors can cause a long lasting change in how the brain processes information.

“A lot of people think of compulsive behaviors as a perturbation of normal habit learning,” Calakos tells mental_floss. She defines habitual behavior as “when you have become so ingrained in behavior that it persists even despite a change in outcome.” For instance, you keep eating after you’re full; you drink too much alcohol after it has produced its initial dopamine release; or you feel the need to wash your hands even after they're clean. Instead, it appears that the brain is actually geared to “favor” habitual behavior.

They trained genetically identical healthy mice to press a lever for a sugar reward. The mice were trained to exhibit either goal-directed behavior (lever pressing decreased when they stopped getting the reward) or a strong sugar habit (the lever pressing persisted when the treats stopped). The researchers then compared the brains of the “sugar habit” mice to those who did not form a habit to see if there were differences in their basal ganglia pathways—one that can be likened to a “go” signal, and one to a “stop” signal.

Prior literature assumed that the “go” neural pathways would be most likely to be activated in conditions of formed habits, but the research found that both pathways were equally excited. However, habits are influenced by the order in which they fired.

“In the habit mice, the go signal cells fired first, and in the goal mice, the stop signal fired first, which means the rate of firing of these cells may influence whether you do or don’t do an action,” Calakos says. “It was exciting seeing that one mechanism for brain plasticity in this region could be a timing shift, which hadn’t been reported before.”

They also found that changes in these stop and go neurons occurred “across the entire region of the basal ganglia,” which may play a part in why a person with one addiction may be more likely to engage in another as well. Calakos says that “an overall gain in excitability of this brain region and a timing shift that favors action expression of go cells correlate with habit,” which suggests that the brain may be primed to elicit go pathways because habits have positive biological outcomes.

“We engage in a habitual behavior more easily," Calakos says. "We don’t give it much thought. We just do it. It’s stimulus based on the environment. Habits are learned, but we don’t think of them that way. Habits are healthy and adaptive, and animals are thought to have habitual behaviors.”

The study also showed that researchers could eventually predict if an animal was going to engage in a habitual behavior depending on if the signals fire for the go or stop system.

Researchers did attempt to break the sugar mice’s habit by a kind of reverse lever-press training—they only rewarded them if they stopped pressing the lever. The mice that were most successful at “quitting” had weaker go cells.

For the next step in research, they’ll be comparing and contrasting the brains of genetically modified compulsive mice with regular mice to see how compulsion and habit are different and similar. The larger goal is to apply what is learned from this research to human substance abuse and addiction, but that’s still in very early stages.

“There are chemical aspects of addiction but there are a lot of situations where habit behaviors may promote unhealthy or harmful behaviors, so the more we understand about the expression of habit and how to suppress or get rid of them, that can be applied to a wide variety of situations,” Calakos says.