Background: Current neurocognitive models of obsessive-compulsive disorder (OCD) implicate dysfunction in top-down inhibitory control mechanisms. Research supports alteration in the functional activity of cortico-basal ganglia-thalamo-cortical loops in OCD, as well as the inferior parietal region, posterior medial cortex, thalamus and cerebellum. The cerebellum, once only known as a region of motor coordination, is now accepted as being highly involved in cognitive regulation as well. Emerging evidence of connectivity between the posterior cerebellum and areas of the brain related to inhibitory functioning, including the basal ganglia, prefrontal, and inferior parietal regions, suggests a potential cerebellar role in OCD-symptomology. In fact, in several disorders that, like OCD, are characterized by impaired cognitive regulation, differences in the size of the cerebellar vermis have been found to exist. Building off of the findings in these related disorders, we targeted our investigation on cerebellar vermal lobules I-V and VI-VII. Despite the strong case for a potential role of the cerebellum based on theory and the known connectivity of the cerebellum, we know of only one study specifically investigating cerebellar morphometry in OCD.
Method and Analysis: Due to the highly irregular anatomical morphology of the cerebellar vermis, and limitations of automated morphometric algorithms, an integrative method of computer-assisted and manual tracing was used to increase accuracy in measuring this area of interest. All imaging and measurements were performed in the Freesurfer imaging software. Cerebellar vermal lobules I-V and VI-VII of an OCD group (n=15) and control group (n=15), were measured by multiple blind-raters trained with a detailed protocol and evaluated for inter-rater reliability. All imaging and neuropsychological data was collected in prior studies.
Hypotheses: We made the following predictions: (i) a reduction in the volume of cerebellar vermal lobules VI-VII associated with a diagnosis of OCD (ii) no significant morphometric differences in cerebellar vermal lobules I-V between subjects with OCD and control subjects, as these areas are largely associated with sensorimotor regulation and, (iii) an association of OCD of greater severity (as assessed by the Y-BOCS) with a greater reduction of vermal tissue in cerebellar lobules VI-VII.
Results: We found no significant differences in the morphometry of cerebellar vermis lobules I-V or VI-VII between subjects with OCD and controls, and no significant relationship between severity of OCD and morphometry. Significant correlations were found in the OCD group between vermal lobules VI-VII and the COWA-FAS test of verbal of fluency and VI-VII and the ROCFT-Copy.
Conclusions: The observations of a possible lack of anatomical differences in the posterior cerebellar vermis between individuals with OCD and control subjects may potentially raise important questions about the underlying biological mechanisms of OCD, however because of the limited power in this finding, the current results cannot be interpreted before an extended investigation is conducted. The significant correlations between the vermal lobules VI-VII in the OCD group and the COWA-FAS and ROCFT-Copy, as well as a relationship between IQ and vermal lobules VI-VII in studies of autism suggest that the relationship between performance in specific cognitive domains and the morphometry of lobules VI-VII in OCD should also be investigated further.
Level of Degree
First Committee Member (Chair)
Kristina Rewin Ciesielski
Second Committee Member
Marco Del Giudice
Third Committee Member
Obsessive-compulsive disorder, cerebellar vermis, inhibition, MRI morphometry, neocerebellum, executive function
Stern, Moriah Eve. "Cerebellar Vermis: Contributions to the Phenomenology of Obsessive-Compulsive Disorder." (2019). https://digitalrepository.unm.edu/psy_etds/277
Available for download on Tuesday, May 11, 2021