Abstract
Resting state fMRI (rs-fMRI) Studies have shown that patients with obsessive-compulsive disorder (OCD) exhibit alterations in cortical excitability and neuronal synchronisation. Amplitude of low frequency fluctuations (ALFF) is a measure used assess the intensity of low frequency oscillations (LFOs) between 0.01-0.1Hz, which are believed to reflect neural activity. Amplitudes of these LFOs are of particular interest as they have shown to range depending on brain area and task. However, ALFF requires standardization and current methods show several shortcomings. To this end, percentage amplitude of fluctuations (PerAF) represents a new approach that has been shown to be valid and more reliable. To attain an improved understanding of OCD pathophysiology, this study investigated alterations of PerAF in a sample of OCD patients. Rs-fMRI data and Yale-Brown Compulsive Obsessive Scale (Y-BOCS) scores of 47 OCD patients and 36 age- and sex-matched healthy controls were obtained. Using RESTplus, the data were preprocessed and PerAF at each voxel was calculated. Groups were compared using t-tests for independent samples, and results were correlated with Y-BOCS scores. Compared to controls, OCD patients showed significantly lower PerAF in the bilateral cingulate gyrus and the right temporal gyrus. Additionally, OCD patients also displayed significantly decreased LFOs signal intensity in the bilateral thalamus and the insula. Notably, these differences showed a trend in correlating with patient-reported compulsion severity and duration of illness. These results indicate that (m)PerAF identifies differences in spontaneous brain activity between OCD patients and healthy controls. Our study shows alterations in LFOs that seem to be neuropathologically relevant for the disorder of OCD but further studies are certainly needed to assess the reliability of this relatively new analysis approach.