OCD: Brain's Habit System Running Amok?
Medscape Medical News
January 07, 2015

Excessive habit formation is linked to increased signaling in the brain region implicated in the pathophysiology of obsessive-compulsive disorder (OCD), new research suggests.

Functional magnetic resonance imaging (fMRI) scans showed a significant association between hyperactivation in the caudate nucleus and excessive habits, as well as an increased urge to perform specific habits, in adult patients with OCD in comparison with their healthy peers.

Led by Claire M. Gillan, PhD, investigators from the University of Cambridge, United Kingdom, told Medscape Medical News that the results suggest that OCD occurs when the brain's habit system "runs amok."

"For a very long time, people thought these irrational beliefs, for example, were driving them to perform compulsions. But we now think that just isn't the case. It may be that the worries and obsessive thoughts present in some patients arise as a consequence of these compulsive behaviors," she said.

Dr Gillan, who is now at New York University, noted that this may also be the case for other compulsive behaviors, including drug and alcohol abuse and binge eating.

"What all these behaviors have in common is the loss of top-down control, perhaps due to miscommunication between regions that control our habit and those such as the prefrontal cortex that normally help control volitional behavior," she said in a release.

"There is this same type of habits dysfunction across different kinds of addiction ― both behavioral and drug related."

The study was published online December 19 in the American Journal of Psychiatry.

OCD Mechanism
For habits to be successfully controlled, the caudate nucleus must "fire correctly," the investigators note.

They have been involved with several studies initiated at the Cambridge Behavioral and Clinical Neuroscience Institute to assess whether OCD compulsions come from an overactive habit system.

In the current research, the investigators examined 37 adult participants with OCD, as shown by scores on the MINI International Neuropsychiatric Interview and the Yale-Brown Obsessive Compulsive Scale (52% women; mean age, 38.1 years) and 33 peers to act as the healthy controls group (43% women; mean age, 37.4 years).

"We wanted to investigate whether there is a basic behavioral deficit in OCD tendency to form habits excessively that makes sense of why people can feel driven to perform actions when they know that the actions are foolish," said Dr Gillan.

All participants underwent fMRIs while performing simple pedal-pressing responses to avoid receiving mild electric shocks to their wrists.

"Following four blocks of training, the authors tested whether the avoidance response had become a habit by removing the threat of shock and measuring continued avoidance," the investigators report.

Brain activity during the tasks was measured in the caudate, the putamen, and the medial orbitofrontal cortex.

During the study, the group with OCD exhibited excessive habit formation, shown by being less likely to stop pedal-pressing habits than the healthy controls group (P = .002).

In addition, these patients responded at a significantly higher rate to both the devalued conditioned stimulus and the valued conditioned stimulus (P = .006 and .03, respectively), and reported "a greater urge to respond to the devalued conditioned stimulus" (P = .001).

Difficult to Treat
Increased brain activity in the caudate nucleus was shown in the OCD group members who exhibited excessive habits ― and was associated with an increased urge to perform habits.

Although there was also significant hyperactivation found in the medial orbitofrontal cortex region during the "acquisition of avoidance" in the overall OCD group vs the healthy controls group (P < .05), this was not a direct result from habit formation.

"Basic imaging work has long since established that the caudate is over-active when the symptoms of OCD are provoked in patients," note the investigators in the release.

"That the habits...trained in these patients in the laboratory also triggered the caudate to over-fire adds weight to the suggestion that compulsions in OCD may be caused by the brain's habit system," they add.

Coinvestigator Trevor Robbins, PhD, said in the same release that although some habits can make life easier, others can go too far and shape preferences and even fears.

"Such conditions ― where maladaptive, repetitive habits dominate our behavior ― are among the most difficult to treat, whether by cognitive behavior therapy or by drugs," said Dr Robbins.

"This study emphasizes the importance of treating OCD early and effectively before the dysfunctional behavior becomes entrenched and difficult to treat," added coinvestigator Barbara Sahakian, PhD.

Dr Gillan agreed, noting that the study's take-home message for clinicians is that they should "consider the nature of this behavioral deficit, this need to perform an action. And if you can break that routine, the habit links break down."

Habits Gone Bad
Asked to comment, Christopher Pittenger, MD, PhD, director of the Yale OCD Research Clinic and associate professor of psychiatry at the Yale University School of Medicine, in New Haven, Connecticut, told Medscape Medical News that although "this is a nice study," it should be looked at in context.

"Over the past 4 years, Claire Gillan, Trevor Robbins, and the rest of their group have put together an impressive series of studies that have examined the same general issue, which is the role of habits and habit learning in OCD," he said. "This is the first study that has used fMRI to look at the neural correlates of the behavioral measures they used previously."

Dr Pittenger, who was not involved with this research, noted that whether a habit involves biting fingernails or taking cocaine, it is very hard to change its maladaptive patterns.

"The hypothesis that these investigators have been exploring is that the repetitive patterns of behavior seen in OCD are habits gone bad. That's a compelling hypothesis that's been out there a while," he said.

"What this paper does is suggest that the brains of people with OCD are primed to form habits. And they looked at what's going on in the brain when that happens," said Dr Pittenger.

Still, he noted that none of this comes as a big surprise.

"We already know the circuitry that's involved with habits and the circuitry that's abnormal in OCD. And that's precisely what they see here: that habit circuitry is hyperactive during the learning phase of OCD," he said.

"But it was a very nice confirmation of the general model that the authors have been developing for the last several years. It's not just that these habits become inflexible because of repetition but rather that it's actually something primed in the brain."

Dr Gillan and four of the eight study authors, as well as Dr Pittenger, have reported no relevant financial relationships. A full list of disclosures from Dr Sahakian, Dr Robbins, and the remaining study author can be found in the original article.

Am J Psychiatr. Published online December 19, 2014. Abstract