Scrupulosity and contamination OCD are not associated with deficits in response inhibition
Introduction
Obsessive-Compulsive Disorder (OCD) is a burdensome neuropsychiatric disorder with a lifetime prevalence rate of approximately 2.3% (Ruscio, Stein, Chiu, & Kessler, 2010). Imaging studies implicate the frontal-striatal circuitry in the pathophysiology of OCD (Pauls, Abramovitch, Rauch, & Geller, 2014), supporting the prevailing cortico-striato-thalamo-cortical (CSTC) model of OCD (Saxena & Rauch, 2000). A complementary substantial body of neuropsychological research, yielding an overall moderate degree of deficits across several neuropsychological domains (Abramovitch et al., 2013, Shin et al., 2014), is characterized by highly inconsistent results (Kuelz, Hohagen, & Voderholzer, 2004). In fact, a recent meta-analysis of neuropsychological test performance in adult OCD revealed statistically significant heterogeneity across most neuropsychological domains that was unaccounted for by clinical, demographic, or factors associated with neuropsychological test administration (Abramovitch et al., 2013).
One of the most highly researched neurocognitive domains in the OCD literature is response inhibition (RI), defined as the ability to inhibit a pre-potent response (Logan, Cowan, & Davis, 1984). The ever-growing interest in RI in OCD stems primarily from imaging studies indicating the prominent role of prefrontal regions, especially the orbitofrontal cortex, in the pathophysiology of OCD (Evans, Lewis, & Iobst, 2004). In fact, RI has frequently been suggested as a candidate endophenotype for OCD (Chamberlain et al., 2005, Menzies et al., 2007). However, as a whole, research on RI in OCD reveals inconsistent, and heterogeneous results (Abramovitch et al., 2013, Kuelz et al., 2004).
Indeed, review of the OCD literature across the three major test paradigms assessing RI reveals that whereas the majority of studies assessing RI using the Stop Signal Task (SST) report significantly reduced performance in OCD samples compared to controls (Chamberlain et al., 2005, Penades et al., 2007, de Wit et al., 2012), only a minority of studies assessing RI using go/no-go (GNG) tests or continuous performance tests (CPT) report differences between OCD and control samples (Abramovitch et al., 2011, Ghisi et al., 2013, Penades et al., 2007, da Rocha et al., 2011). Indeed, a large number of studies report comparable number of commission errors on GNG and CPT tests among OCD individuals compared to controls (Bohne et al., 2008, Krishna et al., 2011, Lee et al., 2009a, Lee et al., 2009b, Page et al., 2009, Thomas et al., 2014, Tolin et al., 2011, Ursu et al., 2003, Watkins et al., 2005), despite evidence for aberrant brain activity while performing RI tasks in OCD (e.g., Page, et al., 2009).
OCD is a heterogeneous disorder that includes various particular clinical presentations including contamination, checking, hoarding, symmetry and ordering and repugnant obsessions (Abramowitz & Jacoby, 2014). It has been speculated that different OCD dimensions – that hypothetically may be associated with different neurocognitive deficiencies - may partially account for variability between neuropsychological studies described above (Abramovitch et al., 2013). Preliminary evidence suggests that some OCD dimensions may be associated with distinct neural correlates (van den Heuvel et al., 2009, Mataix-Cols et al., 2004). Subsequent preliminary neuropsychological studies reported distinct neuropsychological deficits associated with OCD symptom dimensions. For example, Hashimoto et al. (2011) examined neuropsychological correlates of symptom dimensions in a sample of 63 adults with OCD. The authors found that the aggressive/checking dimension was associated with poorer performance only on the trail making test, while the symmetry/ordering dimension was associated with poorer performance on the trail making test and logical (verbal) memory test. Interestingly, the contamination/cleaning dimension was associated with better performance on the latter two tests. Another study reported that deficits in nonverbal memory in OCD may be associated with the checking dimension, but not with contamination/washing (Cha et al., 2008).
A limited number of studies investigated the association between RI and symptom dimensions in OCD. This limited body of literature indicates that there are no performance differences on RI tasks between OCD dimensions, as measured by GNG tests (Khanna and Vijaykumar, 2000, Penades et al., 2007). In fact, OCD symptom dimensions were not found to be differentially associated with performance on other tasks of RI, such as the Stroop and the Stop Signal tasks (Hashimoto et al., 2011, Penades et al., 2007). However, one study found that the checking dimension is associated with a significantly higher number of commission errors on a GNG test than the washing dimension (Omori et al., 2007). In another study using an analogue sample, Lee et al., 2009a, Lee et al., 2009b compared two groups of individuals with symptoms of OCD, using a novel classification of OCD symptoms. Their model does not discriminate between symptom dimension based on content, but by dichotomizing obsessions into autogenous (e.g., sexual, aggressive) and reactive (e.g., contamination, symmetry). Although the authors did not find differences on classic GNG outcome measures, they did find that the autogenous obsessions sample had a significant larger attenuated response inhibition (ARI; Lee, Yost, et al., 2009). ARI is an outcome measure involving RI and set shifting; it is the difference in average response time during a baseline block and a subsequent block for which the target go and no-go stimuli are reversed, thus encompassing both cognitive flexibility/set shifting and RI. As a whole, it appears that small number of studies available reveal inconsistent results concerning the association between RI and OCD symptom dimension, with a trend towards no association.
The aim of the present study is to examine RI using a GNG task in two OCD symptom dimensions, one of which –scrupulosity– has never been subject to a neuropsychological investigation. Scrupulosity, a relatively under-researched dimension in OCD, encompasses obsessions and preoccupation with religious and moral concerns (Abramowitz & Jacoby, 2014). Scrupulosity is often grouped with sexual and aggressive obsessions in a single unacceptable thoughts symptom dimension; however, it is perhaps better thought of as a category of core fear rather than a discrete symptom dimension (Siev & Huppert, in press). For example, a scrupulous individual may fear potentially sinful sexual obsessions (that could be categorized in the unacceptable thoughts dimension) or may engage in excessive checking (that could be categorized in the checking and responsibility for accidental harm dimension) to ensure he performed a religious ritual precisely. Although understudied, approximately 5% of individuals in Western cultures with OCD have primary scrupulosity (Foa and Kozak, 1995, Tolin et al., 2001), and the presence of scrupulosity predicts poor treatment outcome in several studies (e.g., Alonso et al., 2001, Ferrão et al., 2006, Mataix-Cols et al., 2002, Rufer et al., 2005). The second OCD dimension examined in the present study is contamination concerns (also referred to as ‘washing’ or ‘cleaning’). In the context of neuropsychological investigations, this symptom dimension is of particular interest since some studies report intact neuropsychological performance compared to controls (Cha et al., 2008, Nakao et al., 2009), and others report that contamination OCD is associated with better performance on several neuropsychological tasks (Hashimoto et al., 2011, Omori et al., 2007). Individuals with contamination concerns are an appropriate comparison group for this reason. In addition, scrupulosity is assumed to be autogenous and contamination obsessions are reactive (Lee & Kwon, 2003), and Lee et al., 2009a, Lee et al., 2009b compared individuals with autogenous and reactive symptoms using the same task used herein. In sum, the rationale to examine RI in scrupulous individuals derives from the facts that no studies to date have examined the neuropsychology of scrupulosity; scrupulosity is purported to belong to the group of autogenous obsessions, which may be related to RI deficits; and the extant literature on RI in OCD is characterized by mixed results, which may be a function of symptom subtype.
In the present study, we examined rates of commission errors as the primary RI outcome measure, and also evaluated ARI as a secondary measure of RI and set shifting. In light of previous findings, we predicted that individuals with contamination concerns would not differ from healthy controls on measures of RI. Lee et al., 2009a, Lee et al., 2009b found differences on ARI but not commission errors between individuals with autogenous and reactive symptoms using an analogue sample. We therefore expected that scrupulous individuals might demonstrate greater impairment on the measure of ARI, although not commission errors.
Section snippets
Participants
The study sample consisted of 67 individuals meeting inclusion criteria for one of three study groups: scrupulous OCD (n = 29), contamination OCD (n = 19) or healthy controls (n = 19). We initially enrolled 77 individuals; however, nine participants were found ineligible (four of the participants did not meet criteria for OCD severity (their symptoms were sub-clinical), two participants' primary obsessional fear was not scrupulous or contamination-related, one participant did not meet inclusion
Results
The study sample (N = 63) was predominantly Caucasian (n = 58, 92.1%), and consisted of more women (n = 35, 55.6%) than men (n = 28, 43.90%). The mean age of the sample was 33.41 (SD = 12.69). A minority of the sample, (n = 3, 4.8%) identified as Hispanic/Latino. The sample predominantly identified as single (n = 41, 65.1%), with 28.6% married and 6.3% divorced. The sample was also well educated: 66.7% had a college degree and 19.0% had post-college graduate education. 55.5% of the sample was
Discussion
The aim of the present study was to assess RI in scrupulous and contamination OCD compared to non-psychiatric controls using a GNG task. In accordance with our first hypothesis, no difference was found between individuals with contamination OCD and non-psychiatric controls on all GNG indices (reaction time, commission errors, omission errors, and ARI), controlling for depression severity. These results are in accord with previous studies reporting intact neuropsychological task performance
Conclusion
The present study reveals no RI deficits as measured by a GNG test in individuals with scrupulosity and contamination OCD compared to healthy controls. These results are in accordance with the majority of studies examining RI using the GNG and CPT paradigms, and with recent suggestions that RI may not constitute a clinically significant impaired domain in OCD. However, given the different results reported when examining RI using the SST, more research is needed to clarify this controversial
Author note
This research was supported by a grant from the International OCD Foundation to the second author.
The authors thank Michelle Silverman, Natalie Matheny, and Joseph Slimowicz for their work as research assistants, as well as Jason Elias and Leslie Shapiro for their help with recruitment.
All of the authors claim no financial, biomedical or other conflicts of interest pertaining to the present study.
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2018, Journal of Behavior Therapy and Experimental PsychiatryCitation Excerpt :The main results were that there was no predictive value of inhibition, attentional bias or attentional bias variability in the context of contamination-related stimuli over and above baseline symptoms for OC symptoms. This finding is in line with other studies that do not find an association between inhibition or selective attention and OCD (e.g., Morein-Zamir et al., 2013; Rasmussen, Siev, Abramovitch, & Wilhelm, 2016). Moreover, in line with Novara et al. (2011), we did not find that obsessive beliefs predicted OC symptoms, since obsessive beliefs were only a significant predictor for an increase in feelings of mental contamination after OC symptoms induction in the lab and this effect disappeared after taking general baseline OC symptoms into account.
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