Habit formation is one of those everyday phenomena that feels intuitive right up until someone tries to define it precisely. The basic story is familiar: repeat a behavior often enough, and it stops requiring conscious thought, sliding from deliberate decision-making into something closer to automatic pilot. That much has been established for a while. What has remained far murkier is whether a habit, once formed, is simply a faithful copy of the original behavior running on autopilot — or whether the behavior itself keeps changing even after it becomes routine. A new study from Kyoto University, published in Nature Communications, offers a detailed answer, and it points to two separate brain circuits doing two very different jobs.

Part of what has kept this question open for so long is a practical problem: habit formation takes a long time to unfold, which makes it difficult to track behavioral and neural changes within the same individual both before and after a habit takes hold. To get around that obstacle, the Kyoto University team developed a new training protocol that could compress the process, achieving rapid habit formation in mice and allowing researchers to observe the transition directly rather than reconstructing it after the fact.

“Habits are one of the brain’s most mysterious functions, and we often struggle to control them even though they are our own actions,” said Nozomi Asaoka, co-corresponding author on the study. “By uncovering how habits work, we may eventually find ways to take control of them rather than letting them control us.”

The training approach unfolded in two stages, echoing how habits tend to form in humans. Mice were first trained to rely on goal-directed strategies — behavior driven by an explicit expectation of a specific outcome — before undergoing four additional days of training designed to push that behavior toward becoming habitual instead. That two-stage design let the researchers track, in the same individual animals, exactly how the shift from goal-directed to habitual behavior played out in the brain.

What emerged was a division of labor between two distinct neural circuits, each governing a different aspect of habit. The first runs from the anterior cingulate cortex to the retrosplenial cortex, and appears to determine whether a behavior becomes a habit at all — its connections weaken as the transition takes place. The second circuit, running from the lateral orbitofrontal cortex to the central striatum, governs something different: not whether a habit forms, but how vigorously it gets carried out once it does. This second pathway helped explain why individual mice, even after successfully forming the same habit, differed so much in how consistently they performed it. Mice whose neurons in this circuit showed strong responses kept executing the habitual behavior at high levels; those with weaker responses in the same circuit showed reduced execution over time.

The researchers didn’t stop at observing this correlation — they tested it directly, using techniques to manipulate the two pathways artificially. By intervening in each circuit separately, the team was able to either promote the formation of a habit or adjust how strongly it was carried out, effectively demonstrating that the two circuits are doing genuinely distinct jobs rather than reflecting two views of the same underlying process.

The findings complicate a fairly intuitive assumption that has long shaped how scientists think about habits: that repetition works essentially like a photocopier, stamping out increasingly faithful reproductions of an original behavior until the copy becomes automatic. Instead, the Kyoto team’s data show that even after a habit has fully formed, meaningful differences in how often and how intensely it’s expressed persist between individuals — differences that trace back to measurable variation in a specific neural circuit rather than simple noise or incomplete learning.

“Our study has uncovered previously overlooked control mechanisms involved in habit formation, showing what determines how strongly a habit is carried out and helping explain why habits differ from person to person,” said team leader Yasunori Hayashi.

That framing — habits differing from person to person, or in this case from mouse to mouse — points toward where the research is headed next. The team plans to investigate further what actually drives those individual differences in habit intensity, an inquiry the researchers hope could eventually inform both everyday self-improvement efforts and clinical treatment. Habits are, after all, at the center of a wide range of ordinary struggles, from establishing an exercise routine to breaking a tedious but harmful pattern, and the same neural machinery is implicated in more serious clinical conditions, including obsessive-compulsive disorder, where problematic habitual behaviors can become difficult for patients to interrupt or control.

By identifying two separable circuits — one that gates whether a habit forms and another that governs its intensity — the study gives researchers a more precise map of where to intervene, at least in principle, depending on the specific problem at hand. A treatment aimed at helping someone break a compulsive habit might look very different from one aimed at helping someone sustain a beneficial new routine, and having distinct neural targets for “does this become a habit” versus “how strongly is this habit expressed” could eventually allow those two goals to be pursued separately rather than as a single, undifferentiated process.

Endnotes

1. “Dissociable roles of prefrontal plasticity in decision making strategy and execution of habitual behavior.” Nature Communications (2026). DOI: 10.1038/s41467-026-75706-1

2. Kyoto University press release, July 27, 2026, via EurekAlert!: https://www.eurekalert.org/news-releases/1137090