Brain structural imaging correlates of olfactory dysfunction in obsessive-compulsive disorder.

Olfactory dysfunction has been described in obsessive-compulsive disorder (OCD). Brain regions involved in smell processing partially overlap with structures included in the neurobiological models of OCD, although no previous studies have analyzed the neuroanatomical correlates of olfactory dysfunction in this disorder. The aim of our study was to examine the association between regional gray matter volume, as assessed by a voxel-based morphometry analysis of magnetic resonance images (MRI), and olfactory function, as assessed by the Sniffin' Sticks test (SST). Olfactory function was assessed in 19 OCD patients and 19 healthy volunteers. All participants were also scanned in a 1.5-T magnet to obtain T1-weighted anatomical MRIs, which were pre-processed and analyzed with SPM8. Three different correlation models were used to study the association between regional gray matter volumes and olfactory function in the domains assessed by the SST: detection threshold, discrimination, and identification. OCD patients showed a significant impairment in all the domains assessed by the SST. Voxel-based mapping revealed a positive association in healthy controls between detection threshold and the gray matter content of a left anterior cingulate cortex cluster. In OCD patients, a positive correlation was observed between identification errors and the gray matter volume of the left medial orbital gyrus. In a post hoc analysis, these two gray matter regions were shown to be enlarged in OCD patients. Our findings support the idea that olfactory dysfunction in OCD is associated with volumetric changes in brain areas typically implicated in the neurobiology of the disorder.

Neural correlates of obsessive-compulsive related dysfunctional beliefs.

There have been few attempts to integrate neurobiological and cognitive models of obsessive-compulsive disorder (OCD), although this might constitute a key approach to clarify the complex etiology of the disorder. Our study aimed to explore the neural correlates underlying dysfunctional beliefs hypothesized by cognitive models to be involved in the development and maintenance of OCD. We obtained a high-resolution magnetic resonance image from fifty OCD patients and 30 healthy controls, and correlated them, voxel-wise, with the severity of OC-related dysfunctional beliefs assessed by the Obsessive Beliefs Questionnaire-44. In healthy controls, significant negative correlations were observed between anterior temporal lobe (ATL) volume and scores on perfectionism/intolerance of uncertainty and overimportance/need to control thoughts. No significant correlations between OBQ-44 domains and regional gray matter volumes were observed in OCD patients. A post-hoc region-of-interest analysis detected that the ATLs was bilaterally smaller in OCD patients. On splitting subjects into high- and low-belief subgroups, we observed that such brain structural differences between OCD patients and healthy controls were explained by significantly larger ATL volumes among healthy subjects from the low-belief subgroup. Our results suggest a significant correlation between OC-related dysfunctional beliefs and morphometric variability in the anterior temporal lobe, a brain structure related to socio-emotional processing. Future studies should address the interaction of these correlations with environmental factors to fully characterize the bases of OC-related dysfunctional beliefs and to advance in the integration of biological and cognitive models of OCD.