Altered striatal functional gradients in obsessive-compulsive disorder.

Background: Obsessive-compulsive disorder (OCD) is associated with functional alterations in how the striatum interacts with the rest of the brain. However, the characterization of these changes in OCD is incomplete. Mapping functional striatal gradients provides a new opportunity to fill this knowledge gap. These gradients provide a spatial representation of continuous changes in whole-brain connectivity within striatal regions. Thus, OCD-related differences in striatal gradients imply changes in the functional organisation of striatal connections. Methods: We calculated spatial striatal gradients linked to whole brain activity in 52 people with OCD and 45 controls. Gradients were computed with individuals at rest and when they underwent a threat-safety reversal task. Using a longitudinal dataset of 47 people with OCD, we investigated possible associations between changes in striatal gradient topology and fluctuations in symptom severity. Results: Results showed group differences in the main gradient topology at rest, specifically in striatal regions overlapping with the putamen and caudate. Individuals showing a reduction in symptoms over time tended to change their gradient topology in favour of the control participants' average topology. Finally, gradients linked to the appraisal of safety-reversal, but not threat-reversal, showed a group difference in a region separating the right nucleus accumbens and the putamen. Conclusions: This study advances knowledge of striatal connectivity profiles in OCD, supporting a core role of distinct changes in striatal topology in the expression of symptoms. Collectively, these results encourage studies assessing neural mechanisms driving the dynamic reorganisation of striatal topology and the development of therapies leveraging striato-cortical plasticity.