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How the brain makes, and breaks, a habit

Neuroscience study identifies brain chemicals, neural pathway involved

in switching between habitual behavior, deliberate decision-making

Date: May 26, 2016

Source:

University of California – San Diego

Summary:

Not all habits are bad. Some are even necessary. But 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.

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Working with a mouse model, an international team of researchers

demonstrates what happens in the brain for habits to control behavior.

Credit: © gustavofrazao / Fotolia

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 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 the work as a postdoctoral researcher at the National

Institute on Alcohol Abuse and Alcoholism of the National Institutes

of Health. Senior authors on the study are Rui Costa, of the

Champalimaud Centre for the Unknown in Lisbon, and David Lovinger of

the NIAAA/NIH.

The study provides the strongest evidence to date, Gremel said, that

the brain's circuits for habitual and goal-directed action compete for

control — in the orbitofrontal cortex, a decision-making area of the

brain — and that neurochemicals called endocannabinoids allow for

habit to take over, by acting as a sort of 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.

Earlier work by Gremel and Costa had shown that the orbitofrontal

cortex, or OFC, is an important brain area for relaying information on

goal-directed action. They found that by increasing the output of

neurons in the OFC with a technique called optogenetics — precisely

turning neurons on and off with flashes of light — they increased

goal-directed actions. In contrast, when they decreased activity in

the same area with a chemical approach, they disrupted goal-directed

actions and the mice relied on habit instead.

"Habit takes over when the OFC is quieted," Gremel said.

In the current study, since endocannabinoids are known to reduce the

activity of neurons in general, the researchers hypothesized that

endocannabinoids may be quieting or reducing activity in the OFC and,

with it, the ability to shift to goal-directed action. They focused

particularly on neurons projecting from the OFC into the dorsomedial

striatum.

They trained mice to perform the same lever-pressing action for the

same food reward but in two different environments that differentially

bias the development of goal-directed versus habitual actions. Like

humans who don't suffer from neuropsychiatric disorders, healthy mice

will readily shift between performing the same action using a

goal-directed versus habitual action strategy. To stick with the

earlier example of getting home, we can switch the homing autopilot

off and shift to goal-directed behavior when we need to get to a new

or different location.

To test their hypothesis on the role played by endocannabinoids, the

researchers then deleted a particular endocannabinoid receptor, called

cannabinoid type 1, or CB1, in the OFC-to-striatum pathway. Mice

missing these receptors did not form habits — showing the critical

role played by the neurochemicals as well as that particular 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," Gremel said.

"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."

The findings may suggest, the authors say, a new therapeutic target

for people suffering from OCD or addictions: To stop overreliance on

habit and restore the ability to shift from habit to goal-directed

action, it may be helpful to treat the brain's endocannabinoid system

and so reduce habitual control over behavior. Treatment could be

pharmaceutical or might involve behavioral therapy. Further research

is needed.

Story Source:

The above post is reprinted from materials provided by University of

California – San Diego. The original item was written by Inga Kiderra.

Note: Materials may be edited for content and length.

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