White matter structure and symptom dimensions in obsessive-compulsive disorder.

There is evidence that the different symptom dimensions in obsessive-compulsive disorder (OCD) may be mediated by partially distinct neural systems. This DTI study investigated the relationship between symptom dimensions and white matter microstructure. Fractional anisotropy (FA), axial and radial diffusivity was analyzed in relation to the main OCD symptom dimensions. Symptom severity on the obsessing dimension was negatively correlated with FA in the corpus callosum and the cingulate bundle. Severity on the ordering dimension was negatively correlated with FA in, amongst others, the right inferior fronto-occipital fasciculus and the right optic radiation. All correlations were ascribable to alterations in radial diffusivity while there was no association between symptoms and axial diffusivity. Present results illustrate an association between alterations in visual processing tracts and ordering symptoms which are characterized by altered visual processing and increased attention towards irrelevant detail. They also indicate an association between obsessive thoughts and alterations in structures known to be relevant for cognitive control and inhibition. Hence, different symptom dimensions must be taken into account in order to disentangle the neurobiological underpinnings of OCD.