Why do we repeat choices that we know are bad for us? Decision making is characterized by the parallel engagement of two distinct systems, goal-directed and habitual, thought to arise from two computational learning mechanisms, model-based and model-free. The habitual system is a candidate source of pathological fixedness. Using a decision task that measures the contribution to learning of either mechanism, we show a bias towards model-free (habit) acquisition in disorders involving both natural (binge eating) and artificial (methamphetamine) rewards, and obsessive-compulsive disorder. This favoring of model-free learning may underlie the repetitive behaviors that ultimately dominate in these disorders. Further, we show that the habit formation bias is associated with lower gray matter volumes in caudate and medial orbitofrontal cortex. Our findings suggest that the dysfunction in a common neurocomputational mechanism may underlie diverse disorders involving compulsion.

No abstract

BackgroundCognitive behaviour therapy (CBT) is an effective treatment for obsessive–compulsive disorder (OCD) but access to CBT is limited. Internet-based CBT (ICBT) with therapist support is potentially a more accessible treatment. There are no randomized controlled trials testing ICBT for OCD. The aim of this study was to investigate the efficacy of ICBT for OCD in a randomized controlled trial.MethodParticipants (n=101) diagnosed with OCD were randomized to either 10 weeks of ICBT or to an attention control condition, consisting of online supportive therapy. The primary outcome measure was the Yale–Brown Obsessive Compulsive Scale (YBOCS) administered by blinded assessors.ResultsBoth treatments lead to significant improvements in OCD symptoms, but ICBT resulted in larger improvements than the control condition on the YBOCS, with a significant between-group effect size (Cohen's d) of 1.12 (95% CI 0.69–1.53) at post-treatment. The proportion of participants showing clinically significant improvement was 60% (95% CI 46–72) in the ICBT group compared to 6% (95% CI 1–17) in the control condition. The results were sustained at follow-up.ConclusionsICBT is an efficacious treatment for OCD that could substantially increase access to CBT for OCD patients. Replication studies are warranted.

Internet-delivered CBT has specific effects that cannot be attributed only to treatment credibility, expectancy of improvement, therapeutic alliance, or attention. Furthermore, a treatment based on exposure exercises specifically tailored for IBS may be a better treatment option than general stress and symptom management for IBS patients. ICBT is a promising treatment modality for IBS as it can be offered to IBS patients in much larger scale than conventional psychological treatments.

Capsulotomy is effective in reducing OCD symptoms. There is a substantial risk of adverse effects, and the risk may vary between surgical methods. Our findings suggest that smaller lesions are safer and that high radiation doses and multiple procedures should be avoided.