Two neural pathways control our habits

The main difficulty in studying habits is their duration. It is difficult to track behavioral and neural changes in the same subject “before” and “after” habit consolidation. To overcome this limitation, the team developed a method for accelerated habit formation in mice.

The training took place in two stages. At first, the animals were trained to use a purposeful strategy (when an action consciously leads to a specific goal). Then, for four days, additional training was conducted, stimulating the transition to habitual, automatic behavior. This approach allowed researchers to observe the transition from goal-directed actions to habits in the brains of individual mice.

The researchers discovered that two separate neural circuits are responsible for habits, each of which controls a different aspect of behavior:

• The first circuit (neurons from the anterior cingulate cortex to the retrosplenial cortex) determines the very fact of habit formation. As the transition from goal-directed action to habitual action occurs, the connections in this circuit weaken, reflecting a decrease in the need to deliberate the action.
• The second circuit (from the lateral orbitofrontal cortex to the central striatum) is responsible for the intensity of habit execution, i.e. how often and actively a person (or an animal) will perform it. In mice with stronger neural activity in this pathway, the habit was performed more often, and with weak activity, its manifestations decreased.

Scientists confirmed the functional difference between the pathways by artificially manipulating these neural connections. They were able to selectively accelerate the formation of a habit or change the level of its manifestation.

Habit formation is, in the end, a more complex process than previously thought. Repetition does not just fix the action in an unchanged form, but even after the habit is formed, the frequency and volume of its manifestation vary significantly from individual to individual. It is the second neural circuit that explains these individual differences.

According to Yasunori Hayashi, the head of the team, the work reveals previously unaccounted-for habit control mechanisms and helps to understand why they all manifest themselves in different ways.

In the future, scientists plan to find out what factors determine individual differences in the strength of habits. This could help not only to consolidate beneficial habits (such as regular exercise or reading) more effectively, but also to develop new approaches to the treatment of conditions associated with obsessive or problematic habits, in particular, obsessive-compulsive disorder.