Katherine Slinn and Faculty Mentor: Michael Larson, Psychology and Neuroscience
This project was an in-depth statistical analysis of previously collected data in order to explore the hypothesis that obsessive-compulsive disorder (OCD) is associated with a decrease in the ability to regulate behavior and to apply top-down cognitive control. OCD has been diagnosed in approximately 2.2 million Americans, typically appearing in early adulthood. Approximately half of these cases show severe functional impairment (Kessler, Chiu, Demler, & Walters, 2005). Obsessions are defined as unwanted and recurrent thoughts or impulses, and compulsions are repetitive behaviors that are driven by these obsessions, such as ordering or counting (American Psychiatric Association, 2013). 20% to 30% of adults with OCD have poor insight, meaning they are unaware of the severity of their illness, which has been shown to correlate with the inability to control OCD tendencies (Jacob, Larson & Storch, 2014). Emerging literature suggests that OCD-related impairment is related to poor cognitive control, which is the ability to regulate thoughts and behaviors in accord with internal goals (Miller & Cohen, 1999). However, it is unclear what specific aspects of cognitive control contribute to OCD-related difficulties and functional impairment. We aimed to examine the association between cognitive control abilities, functional impairment, and OCD symptom severity. A better understanding of a patient’s cognitive ability may explain the inability to overcome compulsions that affect day-to-day functioning.
Fifty-seven participants were initially recruited from the community and included 26 healthy participants and 31 participants with a diagnosis of OCD. The mean age of the participants was 25.2 years, with 15.15 years of education. We tested if cognitive control was significantly impaired in OCD participants compared to a demographically-matched control group using the AX-CPT task. The task measures a participant’s ability to process information by providing an initial stimulus (“A” or “B”), followed by a secondary stimulus (“X” or “Y”). A response should be given if an “A” is followed by an “X”, requiring participants to remember the previous cue and withhold their response accordingly if the incorrect pattern was shown. We measured performance on this task using accuracy rates for each trial type and median reaction times of correct responses. We also collected multiple measures of functional deficits and symptom severity; a secondary aim of the analysis was to determine the relationship between inhibitory control and OCD-related functional impairment and symptom severity. Accuracy rates and median RTs were separately analyzed using two 2-group x 4-trial type repeated measures analysis of variance (ANOVA).
Control participants and OCD patients were well matched for age, t(47)=-0.21 p=0.83, and education, t(47)=1.31 p=0.20. The average Y-BOCS score for OCD participants was 17.41, a mild to moderate level of OCD. Of the 57 participants, six were excluded due to accuracy rates less than 50%. The OCD and control participants were well matched for for accuracy, there was a significant main effect of trial type, F(3,150)=15.88 p<0.001. Tests of simple effects indicate AX performance was better than AY(p=0.002) and BX(p=0.031), but worse than the control by condition(p<0.001). The main effect of accuracy was non-significant, F(1,50)=0.005 p=0.94. Similarly, the Group x Trial interaction was non-significant, F(3,150)=1.018, p=0.387. For median RTs, there was also a main effect of trial type, F(3,150)=91.76 p<0.001. AX trials were faster than AY(p<0.001) and BX(p=0.03), but nearly identical to BY trials(p=0.99). The main effect of group was again non-significant, F(1,50)=0.017, p=0.897. Similarly, the Group x Trial interaction was non-significant, F(3,150)=0.57, p=0.636.
The significant main effects for both accuracy rates and RTs follow a pattern typical for the AX-CPT task. Notably, however, there were no differences between the control and OCD participant groups, suggesting no decrease in cognitive control related to OCD. Limitations include the small sample size due to the difficulty of recruiting participants diagnosed with OCD and the six participants who were excluded due to low accuracy rates, a result of not understanding the task instructions. We also acknowledge the low symptom severity of our OCD participants, shown by the low average Y-BOCS score, making it difficult to generalize the results to all patients with OCD.
In conclusion, performance of participants with OCD did not differ from controls in our AX-CPT cognitive control task. This suggests that there is no difference between cognitive functioning in controls and OCD patients. However, our findings cannot be conclusive due to our OCD participants having only mild to moderate symptoms; more severe cases of OCD may have inherently different cognitive functioning, and their performance should be explored. We are also limited by our small sample size, a result of being unable to recruit more participants from the community with an OCD diagnosis. Further studies with larger sample size are required to further study cognitive impairment due to OCD. These studies could also include using EEG or fMRI technology to examine the actual brain processing used for cognitive control, in order to examine if these are the same for OCD and control participants also.
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Washington, DC: Author.
Jacob M.L., Larson M.J., Storch E.A. (2014). Insight in adults with obsessive compulsive disorder. Comprehensive Psychiatry, 55(4), 896-903.
Kessler R.C., Chiu W.T., Demler O., & Walters E.E. (2005). Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the national comorbidity survey replication. Archives of General Psychiatry, 62, 617-627.
Miller E.K., Cohen J.D. (2001). An integrative theory of prefrontal cortex function. Annual Review of Neuroscience, 24, 167-202.