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How the brain makes — and breaks — a habit

Neuroscience is identifying brain chemicals and neural paths that help us switch from habitual behavior into deliberate decision making.

Not all habits are bad. Some are even necessary. It's a good thing, for example, that we can find our way home on "autopilot" or wash our hands without having to ponder every step. But an inability to switch from acting habitually to acting in a deliberate way can underlie addiction and obsessive compulsive disorders.

Working with a mouse model, an international team of researchers demonstrates what happens in the brain for habits to control behavior.

The study is published in Neuron and was led by Christina Gremel, assistant professor of psychology at the University of California San Diego, who began his work as a postdoctoral researcher at the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health or the NIAAA/NIH. Additional senior authors on the study are Rui Costa, of the Champalimaud Centre for the Unknown in Lisbon, and David Lovinger, also of the NIAAA/NIH.

The study provides the strongest evidence to date, the brain's circuits for habitual and goal-directed action compete for control.

In the orbitofrontal cortex, a decision-making area of the brain, neurochemicals - endocannabinoids, allow for habit to take over. They act to put a brake on the goal-directed circuit.

Endocannabinoids are a class of chemicals produced naturally by humans and other animals. Receptors for endocannabinoids are found throughout the body and brain, and the endocannabinoid system is implicated in a variety of physiological processes - including appetite, pain sensation, mood and memory. It is also the system that mediates the psychoactive effects of cannabis (marijuana).

Earlier work by Gremel and Costa showed that the orbitofrontal cortex, or OFC, is an important brain area for relaying information on goal-directed activities. They found that by increasing the output of neurons in the OFC with optogenetics — a technique involving the precise turning off and on of neurons with flashes of light — they increased goal-directed actions. In contrast, when they decreased activity in the same area using a chemical approach, they disrupted goal-directed actions and the mice reverted to habitual behaviors instead.

"Habit takes over when the OFC is quieted."

Christina Gremel PhD, Assistant Professor of Psychology, University of California San Diego, California, USA

As endocannabinoids are known to slow the activity of neurons in general, researchers hypothesized that endocannabinoids may be able to quiet or reduce activity in the OFC, and help the shift to goal-directed action. They focused particularly on neurons projecting from the OFC into the dorsomedial striatum.

So they trained mice to perform a lever-pressing action for food rewards but in two different environments; one with a bias towards goal-directed behavior — versus an environment leaning toward habitual behaviors. Like humans who don't suffer from neuropsychiatric disorders, healthy mice can easily shift between actions using a goal-directed strategy versus one using a habitual, repetitive strategy.

But in a test of "going home" behavior, a mouse's homing autopilot was switched off and shifted to a goal-directed behavior sending the mouse to a different location. Researchers had deleted a particular set of endocannabinoid receptors in the OFC to striatum pathway. Mice missing these receptors did not perform the habitual "going home" behavior — reflecting the critical role played by neurochemicals on that particular, critical, pathway.

"We need a balance between habitual and goal-directed actions. For everyday function, we need to be able to make routine actions quickly and efficiently, and habits serve this purpose.

"However, we also encounter changing circumstances, and need the capacity to 'break habits' and perform a goal-directed action based on updated information. When we can't, there can be devastating consequences."

Christina Gremel PhD

According to the authors, these findings suggest a new therapeutic target for people suffering from OCD and even addictions. Specifically, in order to stop over-reliance on habit, recipients need to restore their ability to shift from habit to goal-directed activity. In help make this switch, it may be useful to treat the endocannabinoid system and reduce habitual control over behavior. Treatment could be pharmaceutical or involve behavioral therapy, but further research is sugested by Gremel and Costa.

Abstract Highlights
•OFC-DS circuit mediates goal-directed control of actions
•Inhibition of OFC-DS transmission is necessary for habitual action control
•Selective deletion of CB1 receptors in OFC-DS neurons prevents habit formation
•Endocannabinoid-mediated weakening of goal-directed circuits allows for habit formation

Everyday function demands efficient and flexible decision-making that allows for habitual and goal-directed action control. An inability to shift has been implicated in disorders with impaired decision-making, including obsessive-compulsive disorder and addiction. Despite this, our understanding of the specific molecular mechanisms and circuitry involved in shifting action control remains limited. Here we identify an endogenous molecular mechanism in a specific cortical-striatal pathway that mediates the transition between goal-directed and habitual action strategies. Deletion of cannabinoid type 1 (CB1) receptors from cortical projections originating in the orbital frontal cortex (OFC) prevents mice from shifting from goal-directed to habitual instrumental lever pressing. Activity of OFC neurons projecting to dorsal striatum (OFC-DS) and, specifically, activity of OFC-DS terminals is necessary for goal-directed action control. Lastly, CB1 deletion from OFC-DS neurons prevents the shift from goal-directed to habitual action control. These data suggest that the emergence of habits depends on endocannabinoid-mediated attenuation of a competing circuit controlling goal-directed behaviors.

Authors in addition to Gremel, Costa and Lovenger, the study's co-authors are Jessica Chancey, Brady Atwood and Guoxiang Luo of the NIAA; Rachael Neve of the Massachusetts Institute of Technology; and Charu Ramakrishnan and Karl Deisseroth of Stanford University.

This research was supported by the NIAAA Division of Intramural Clinical and Biological Research, ERA-NET, European Research Council (COG 617142) and HHMI (IEC 55007415) grants to Costa and a Pathway to Independence Award (R00 AA021780) and NARSAD Young Investigator Grant from the Brain & Behavior Research Foundation to Gremel.
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Jun 2, 2016   Fetal Timeline   Maternal Timeline   News   News Archive   

Researchers believe the orbitofrontal cortex (OFC) may be treatable with endocannabinoids
in order to shift from habitual behavior into goal-directed action.
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