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How the brain makes — and breaks — a habit
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.
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.
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.
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.
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.
Researchers believe the orbitofrontal cortex (OFC) may be treatable with endocannabinoids
in order to shift from habitual behavior into goal-directed action.
Image Credit: Wikipedia