Age of onset of obsessive-compulsive disorder differentially affects white matter microstructure.

Previous diffusion MRI studies have reported mixed findings on white matter microstructure alterations in obsessive-compulsive disorder (OCD), likely due to variation in demographic and clinical characteristics, scanning methods, and underpowered samples. The OCD global study was created across five international sites to overcome these challenges by harmonizing data collection to identify consistent brain signatures of OCD that are reproducible and generalizable. Single-shell diffusion measures (e.g., fractional anisotropy), multi-shell Neurite Orientation Dispersion and Density Imaging (NODDI) and fixel-based measures, were extracted from skeletonized white matter tracts in 260 medication-free adults with OCD and 252 healthy controls. We additionally performed structural connectome analysis. We compared cases with controls and cases with early (<18) versus late (18+) OCD onset using mixed-model and Bayesian multilevel analysis. Compared with healthy controls, adult OCD individuals showed higher fiber density in the sagittal stratum (B[SE] = 0.10[0.05], P = 0.04) and credible evidence for higher fiber density in several other tracts. When comparing early (n = 145) and late-onset (n = 114) cases, converging evidence showed lower integrity of the posterior thalamic radiation -particularly radial diffusivity (B[SE] = 0.28[0.12], P = 0.03)-and lower global efficiency of the structural connectome (B[SE] = 15.3[6.6], P = 0.03) in late-onset cases. Post-hoc analyses indicated divergent direction of effects of the two OCD groups compared to healthy controls. Age of OCD onset differentially affects the integrity of thalamo-parietal/occipital tracts and the efficiency of the structural brain network. These results lend further support for the role of the thalamus and its afferent fibers and visual attentional processes in the pathophysiology of OCD.

Measurement fidelity of clinical assessment methods in a global study on identifying reproducible brain signatures of obsessive-compulsive disorder.

OBJECTIVE: To describe the steps of ensuring measurement fidelity of core clinical measures in a five-country study on brain signatures of obsessive-compulsive disorder (OCD). METHOD: We collected data using standardized instruments, which included the Yale-Brown Obsessive-Compulsive Scale (YBOCS), the Dimensional YBOCS (DYBOCS), the Brown Assessment of Beliefs Scale (BABS), the 17-item Hamilton Depression Scale (HAM-D), the Hamilton Anxiety Scale (HAM-A), and the Structured Clinical Interview for DSM-5 (SCID). Steps to ensure measurement fidelity included translating instruments, developing a clinical decision manual, and continuing reliability training with 11-13 transcripts of each instrument by 13 independent evaluators across sites over 4 years. We use multigroup confirmatory factor analysis (MGCFA) to report interrater reliability (IRR) among the evaluators and factor structure for each scale in 206 participants with OCD. RESULTS: The overall IRR for most scales was high (ICC > 0.94) and remained good to excellent throughout the study. Consistent factor structures (configural invariance) were found for all instruments across the sites, while similarity in the factor loadings for the items (metric invariance) could be established only for the DYBOCS and the BABS. CONCLUSIONS: It is feasible to achieve measurement fidelity of clinical measures in multisite, multilinguistic global studies, despite the challenges inherent to such endeavors. Future studies should not only report IRR but also consider reporting methods of standardization of data collection and measurement invariance to identify factor structures of core clinical measures. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Cross-national harmonization of neurocognitive assessment across five sites in a global study.

OBJECTIVE: Cross-national work on neurocognitive testing has been characterized by inconsistent findings, suggesting the need for improved harmonization. Here, we describe a prospective harmonization approach in an ongoing global collaborative study. METHOD: Visuospatial N-Back, Tower of London (ToL), Stop Signal task (SST), Risk Aversion (RA), and Intertemporal Choice (ITC) tasks were administered to 221 individuals from Brazil, India, the Netherlands, South Africa, and the USA. Prospective harmonization methods were employed to ensure procedural similarity of task implementation and processing of derived task measures across sites. Generalized linear models tested for between-site differences controlling for sex, age, education, and socioeconomic status (SES). Associations with these covariates were also examined and tested for differences by site with site-by-covariate interactions. RESULTS: The Netherlands site performed more accurately on N-Back and ToL than the other sites, except for the USA site on the N-Back. The Netherlands and the USA sites performed faster than the other three sites during the go events in the SST. Finally, the Netherlands site also exhibited a higher tolerance for delay discounting than other sites on the ITC, and the India site showed more risk aversion than other sites on the RA task. However, effect size differences across sites on the five tasks were generally small (i.e., partial eta-squared < 0.05) after dropping the Netherlands (on ToL, N-Back, ITC, and SST tasks) and India (on the RA task). Across tasks, regardless of site, the N-Back (sex, age, education, and SES), ToL (sex, age, and SES), SST (age), and ITC (SES) showed associations with covariates. CONCLUSIONS: Four out of the five sites showed only small between-site differences for each task. Nevertheless, despite our extensive prospective harmonization steps, task score performance deviated from the other sites in the Netherlands site (on four tasks) and the India site (on one task). Because the procedural methods were standardized across sites, and our analyses were adjusted for covariates, the differences found in cognitive performance may indicate selection sampling bias due to unmeasured confounders. Future studies should follow similar cross-site prospective harmonization procedures when assessing neurocognition and consider measuring other possible confounding variables for additional statistical control. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Year of Zoom in a Year of Doom: Lessons Learned Delivering ERP Remotely During the COVID-19 Pandemic.

In response to the COVID-19 pandemic and consequential shutdown measures, many mental health professionals started providing therapy to patients exclusively via telehealth. Our research center, which specializes in studying and treating obsessive-compulsive disorder (OCD), historically has provided in-person exposure and response prevention (ERP) to adults with OCD, but shifted to telehealth during the pandemic. Unlike in other modes of talk therapy, ERP's emphasis on therapist-supervised exposures presented unique opportunities and challenges to delivering treatment entirely via a virtual platform. This paper provides case examples to illustrate lessons we learned delivering ERP exclusively via telehealth in New York from March 2020 through June 2021 and offers recommendations for future study and practice. Though we observed a number of drawbacks to fully remote ERP, we also discovered advantages to delivering ERP this way, meriting additional research attention.

Resilience predicts positive mental health outcomes during the COVID-19 pandemic in New Yorkers with and without obsessive-compulsive disorder.

There has been substantial concern about the mental health effects of the COVID-19 pandemic, particularly for those with obsessive-compulsive disorder (OCD) given the overlap between OCD symptoms (e.g., excessive handwashing) and appropriate disease prevention measures. However, the pandemic has demonstrated heterogeneous mental health effects, suggesting that individual-level factors could play a role in buffering or exacerbating its deleterious impact. This study aimed to understand how individual differences in resilience were associated with trajectories of obsessive-compulsive, depression, and anxiety symptoms among healthy adults and those with OCD residing in New York City, considered the epicenter of the pandemic in the United States at its onset. The sample consisted of healthy individuals (n = 30) and people with OCD (n = 33) who completed clinical interviews and self-report questionnaires that assessed baseline resilience, OCD symptoms, depression, anxiety, and perceived positive effects of the pandemic at four assessment timepoints: baseline (April 2020) and one, two, and six months later. Linear mixed-effects growth models revealed that greater resilience was associated with stable trajectories of symptoms over time. Conversely, less resilience was associated with worsening obsessive-compulsive symptoms from the two-month to six-month assessment timepoints and worsening depressive symptoms at six months across both groups, and with worsening anxiety symptoms in individuals with OCD at six months. Resilience was correlated with the ability to appreciate "silver linings" of the pandemic. These findings highlight resilience as a potential treatment target for bolstering mental health outcomes among individuals with and without psychopathology during sustained and unprecedented periods of stress.

Integrating Exposure and Response Prevention With a Mobile App to Treat Obsessive-Compulsive Disorder: Feasibility, Acceptability, and Preliminary Effects.

Many individuals with obsessive-compulsive disorder (OCD) do not receive evidence-based care (specifically exposure and ritual prevention; EX/RP) due to barriers such as a lack of EX/RP-trained clinicians, geographic obstacles, and the cost and time associated with the treatment. Offering an integrated treatment model consisting of brief in-person therapy coupled with a mobile application (app) might be one way to increase access to and reduce the time burden (to clinicians and patients) of EX/RP. This pilot trial evaluated the feasibility, acceptability, and clinical effects of such a treatment program for adults with OCD. Thirty-three participants enrolled in the 8-week open trial. The integrated treatment program consisted of 3 to 5 in-person sessions followed by weekly phone calls supported by a mobile app (nOCD). Participants were evaluated by trained raters and completed self-report measures at baseline, midtreatment, posttreatment and 2-month follow-up; the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) was the primary outcome. This integrated treatment program was feasible and acceptable to participants. Of the 33 study entrants, 14 (42%) responded to treatment (Y-BOCS decrease ≥35% with CGI- of 1 or 2), and 8 (24%) achieved minimal symptoms (i.e., Y-BOCS ≤12). At 2-month follow-up (n=20), 7/20 (35%) met criteria for treatment response, and 3/20 (15.0%) met criteria for treatment remission. Although preliminary, this model warrants further study as an efficacious and resource-efficient way to deliver EX/RP for some patients with OCD.

Is my patient too sad to approach their fear? Depression severity and imaginal exposure outcomes for patients with OCD.

BACKGROUND AND OBJECTIVES: There is conflicting research on how comorbid depression impacts the treatment of obsessive compulsive disorder (OCD) with exposure with response prevention. To better understand this relationship, the current study tests theoretical claims that greater depression limits motivation to engage in exposures, restricts habituation, and interferes with adaptive learning. METHODS: Fifty-one individuals with OCD completed a diagnostic interview and self-report questionnaires assessing depression symptom severity and then participated in a standardized imaginal exposure protocol, in which they repeatedly approached an idiosyncratic fear deemed "moderately anxiety-provoking." RESULTS: Contrary to expectations, linear regression models indicated that depression symptom severity was not independently associated with motivation, subjective or objective within-session habituation or adaptive learning outcomes. However, the perceived likelihood of the best-case scenario occurring as a result of the exposure moderated the relationship between depression severity and motivation to engage in the exposure exercise. LIMITATIONS: Use of a one-session exposure protocol precludes conclusions regarding how depression is associated with outcomes in a full ERP treatment. CONCLUSIONS: Depression symptom severity was not independently associated with motivation, habituation, or adaptive learning. The observed non-significant effects suggest that degree of depression, on its own, is not a meaningful indicator of how patients with OCD will fare an exposure intervention.

Toward identifying reproducible brain signatures of obsessive-compulsive profiles: rationale and methods for a new global initiative.

BACKGROUND: Obsessive-compulsive disorder (OCD) has a lifetime prevalence of 2-3% and is a leading cause of global disability. Brain circuit abnormalities in individuals with OCD have been identified, but important knowledge gaps remain. The goal of the new global initiative described in this paper is to identify robust and reproducible brain signatures of measurable behaviors and clinical symptoms that are common in individuals with OCD. A global approach was chosen to accelerate discovery, to increase rigor and transparency, and to ensure generalizability of results. METHODS: We will study 250 medication-free adults with OCD, 100 unaffected adult siblings of individuals with OCD, and 250 healthy control subjects at five expert research sites across five countries (Brazil, India, Netherlands, South Africa, and the U.S.). All participants will receive clinical evaluation, neurocognitive assessment, and magnetic resonance imaging (MRI). The imaging will examine multiple brain circuits hypothesized to underlie OCD behaviors, focusing on morphometry (T1-weighted MRI), structural connectivity (Diffusion Tensor Imaging), and functional connectivity (resting-state fMRI). In addition to analyzing each imaging modality separately, we will also use multi-modal fusion with machine learning statistical methods in an attempt to derive imaging signatures that distinguish individuals with OCD from unaffected siblings and healthy controls (Aim #1). Then we will examine how these imaging signatures link to behavioral performance on neurocognitive tasks that probe these same circuits as well as to clinical profiles (Aim #2). Finally, we will explore how specific environmental features (childhood trauma, socioeconomic status, and religiosity) moderate these brain-behavior associations. DISCUSSION: Using harmonized methods for data collection and analysis, we will conduct the largest neurocognitive and multimodal-imaging study in medication-free subjects with OCD to date. By recruiting a large, ethno-culturally diverse sample, we will test whether there are robust biosignatures of core OCD features that transcend countries and cultures. If so, future studies can use these brain signatures to reveal trans-diagnostic disease dimensions, chart when these signatures arise during development, and identify treatments that target these circuit abnormalities directly. The long-term goal of this research is to change not only how we conceptualize OCD but also how we diagnose and treat it.

Affective forecasting accuracy in obsessive compulsive disorder.

BACKGROUND: Research indicates that people suffering from obsessive compulsive disorder (OCD) possess several cognitive biases, including a tendency to over-estimate threat and avoid risk. Studies have suggested that people with OCD not only over-estimate the severity of negative events, but also under-estimate their ability to cope with such occurrences. What is less clear is if they also miscalculate the extent to which they will be emotionally impacted by a given experience. AIMS: The aim of the current study was twofold. First, we examined if people with OCD are especially poor at predicting their emotional responses to future events (i.e. affective forecasting). Second, we analysed the relationship between affective forecasting accuracy and risk assessment across a broad domain of behaviours. METHOD: Forty-one OCD, 42 non-anxious, and 40 socially anxious subjects completed an affective forecasting task and a self-report measure of risk-taking. RESULTS: Findings revealed that affective forecasting accuracy did not differ among the groups. In addition, there was little evidence that affective forecasting errors are related to how people assess risk in a variety of situations. CONCLUSIONS: The results of our study suggest that affective forecasting is unlikely to contribute to the phenomenology of OCD or social anxiety disorder. However, that people over-estimate the hedonic impact of negative events might have interesting implications for the treatment of OCD and other disorders treated with exposure therapy.

Standard of proof and intolerance of uncertainty in obsessive-compulsive disorder and social anxiety disorder.

BACKGROUND AND OBJECTIVES: Researchers have identified intolerance of uncertainty (IU) as a dysfunctional thought that contributes to OCD. Case examples of OCD suggest that uncertainty and anxiety persist despite low likelihoods of feared outcomes. In this study we examined how people with OCD react to minimal amounts of uncertainty relative to non-anxious individuals and a clinical comparison group of people with social anxiety disorder (SAD). METHODS: We created a questionnaire to measure the distress people feel when there is only minimal uncertainty regarding a given outcome and if they prefer situations with the certainty of negative outcomes in the present versus living with uncertainty. Part two of our study tested whether IU is related to performance on neutral and idiographic versions of the Beads Task. RESULTS: OCD and SAD subjects reacted to hypothetical scenarios involving minimal risk with greater negative affect than did non-anxious subjects; however, after repeating analyses to account for comorbid disorders, OCD subjects' scores did not differ from those of non-anxious subjects. Only SAD subjects showed a preference for negative information in the present versus the uncertainty of a future outcome. Part two of our study revealed that self-reported IU was only marginally associated with performance on the neutral Beads Task. LIMITATIONS: High rates of comorbidity made it difficult to identify the specific relationship of IU with other anxiety disorders. CONCLUSIONS: IU for general, non-OCD specific scenarios may not figure prominently in all individuals with OCD, but rather may play a larger, more consistent role in anxiety disorders such as SAD. Additionally, the number of beads or words viewed on Beads Task may be an inadequate behavioral measure of IU.

Exposure and response prevention for obsessive-compulsive disorder: A review and new directions.

Obsessive-compulsive disorder (OCD) is characterized by distressing thoughts and repetitive behaviors that are interfering, time-consuming, and difficult to control. Although OCD was once thought to be untreatable, the last few decades have seen great success in reducing symptoms with exposure and response prevention (ERP), which is now considered to be the first-line psychotherapy for the disorder. Despite these significant therapeutic advances, there remain a number of challenges in treating OCD. In this review, we will describe the theoretical underpinnings and elements of ERP, examine the evidence for its effectiveness, and discuss new directions for enhancing it as a therapy for OCD.

Utilizing Exposure and Response Prevention to Address Poor Insight in Obsessive-Compulsive Disorder.

Studies indicate that approximately 9%-30% of adults diagnosed with obsessive-compulsive disorder have poor insight into their symptoms. That is, they fail to recognize the excessiveness or irrationality of the obsessive thoughts or their compulsive behaviors. Poor insight in OCD is associated with more severe symptoms, earlier age of illness onset, longer illness duration, and higher rates of comorbid depression. Moreover, some studies have also reported that patients with poor insight are less likely than are those with good or fair insight to respond to first-line treatments such as exposure and response prevention (ERP). Despite the clinical relevance of poor insight, very little research has focused on how to enhance therapy with strategies specifically used to target it. In this report, we use a case study to demonstrate how different techniques can be emphasized or integrated with standard ERP to improve treatment outcomes for this subset of patients.

A Multisite Study of Family Functioning Impairment in Pediatric Obsessive-Compulsive Disorder.

OBJECTIVE: Familial aspects of pediatric obsessive-compulsive disorder (OCD), including accommodation and treatment, have received notable and warranted attention. However, individual perspectives of its repercussions on family functioning, including emotional and occupational parental burden, have not been closely examined. The present study details this topic using a large multicenter sample. METHOD: Participants included 354 youth affected with OCD and their mothers and fathers ascertained through OCD programs in Boston, Massachusetts (n = 180) and Vancouver, British Columbia (n = 174). The validated OCD Family Functioning Scale and standard OCD measurements were completed. Descriptive, between-site, and cross-perspective comparative analyses were followed by regression model testing to predict family impairment. RESULTS: Family functioning was negatively affected from youth, mother, and father perspectives. Impairment was reportedly more extensive at the time of worst OCD severity and was greater from maternal versus paternal viewpoints. Most frequently affected family tasks and implicated OCD symptoms included morning and bedtime routines and intrusive thoughts. Emotional repercussions in all members included stress and anxiety, followed by frustration or anger in youth and sadness in parents. Nearly half of mothers and one third of fathers reported daily occupational impairment. Compared with youth self-report, parents perceived fewer social and academic effects on their child. Family accommodation most consistently predicted family impairment, especially from parent perspectives. OCD and compulsion severity, contamination and religious obsessions, and comorbidities also predicted various perspectives of family subdomain impairment. CONCLUSION: This study quantitatively details the pervasive burden that pediatric OCD places on families, as reported from complementary relative perspectives. Further attention to this topic is warranted in clinical and research realms.

A Theoretical review of cognitive biases and deficits in obsessive-compulsive disorder.

During the past 30 years, experimental psychopathologists have conducted many studies aiming to elucidate the cognitive abnormalities that may figure in the etiology and maintenance of OCD. In this paper, we review research on both dysfunctional beliefs and cognitive deficits in OCD, as findings from both traditional self-report and information-processing approaches provide distinct sources of information concerning cognitive abnormalities. First, we discuss dysfunctional beliefs and metacognitive beliefs implicated in the disorder. Research has identified a number of maladaptive appraisals (e.g., heightened responsibility) and metacognitive beliefs (e.g., need to control one's thoughts) that are associated with the disorder, yet these are not invariably present in all cases of OCD. Next, we review the literature on memory and attentional deficits and biases in OCD. This line of research shows inconsistent evidence for deficits in memorial and attentional processes, but does indicate that people with the disorder have memory and attention biases that may be related to metacognitive beliefs about their ability to remember and attend to stimuli. Finally, we discuss recent work that suggests that people with OCD have reduced access to internal states, thus causing them to engage in rituals to resolve persistent uncertainty. Implications and future directions are discussed.

Creativity, personality, and hoarding behavior.

Compulsive hoarding is a debilitating illness that is characterized by excessive collection of and failure to discard items, irrespective of their uselessness or hazardousness. Anecdotal evidence suggests that individuals who hoard may be more creative than individuals without hoarding behavior; however, this hypothesis has never been tested empirically. In the present study, we examined the relationship between hoarding symptoms and performance on a series of creativity measures. We also explored the extent to which hoarding symptoms were associated with factors such as personality, impulsivity, distress tolerance, and attitudes about money and the environment. Our findings revealed no significant associations between hoarding behavior and any measure of creativity. Hoarding behavior was also unrelated to attitudes about money or concern about the environment. However, consistent with previous research, hoarding tendencies were correlated with higher levels of neuroticism and impulsivity, as well as with lower levels of conscientiousness and distress tolerance. Implications of these findings are discussed.

Theory of mind impairments in social anxiety disorder.

Social anxiety disorder (SAD) is a common psychiatric disorder characterized by a persistent, excessive fear and avoidance of social and performance situations. Research on cognitive biases indicates individuals with SAD may lack an accurate view of how they are perceived by others, especially in social situations when they allocate important attentional resources to monitoring their own actions as well as external threat. In the present study, we explored whether socially anxious individuals also have impairments in theory of mind (ToM), or the ability to comprehend others' mental states, including emotions, beliefs, and intentions. Forty socially anxious and 40 non-socially-anxious comparison participants completed two ToM tasks: the Reading the Mind in the Eyes and the Movie for the Assessment of Social Cognition. Participants with SAD performed worse on ToM tasks than did non-socially-anxious participants. Relative to comparison participants, those with SAD were more likely to attribute more intense emotions and greater meaning to what others were thinking and feeling. These group differences were not due to interpretation bias. The ToM impairments in people with SAD are in the opposite direction of those in people with autism spectrum conditions whose inferences about the mental states of other people are absent or very limited. This association between SAD and ToM may have important implications for our understanding of both the maintenance and treatment of social anxiety disorder.

Emotional distress and pain tolerance in obsessive-compulsive disorder.

BACKGROUND AND OBJECTIVES: Physical pain can reduce emotional distress, perhaps especially the psychic pain of guilt. This implies that people who continually experience guilt may exhibit greater tolerance for pain relative to people who do not. METHODS: To test this hypothesis, we administered a pressure algometer procedure to assess pain tolerance in patients with obsessive-compulsive disorder (OCD) plagued by moral obsessions (e.g., concerns about harming others, violating religious values), in patients with OCD with non-moral obsessions (e.g., regarding contamination and symmetry), and in healthy comparison subjects. RESULTS: The results indicated that the OCD groups did not differ in levels of guilt, emotional distress tolerance, or in pain endurance. However, when we collapsed across subtypes, OCD subjects endured pain significantly longer than did healthy subjects. LIMITATIONS: Limitations included small sample size and use of a sample with complex OCD symptoms that were, in some instances, difficult to categorize. CONCLUSIONS: The results suggest that individuals with severe OCD might be willing to endure physical pain as a distraction from emotional distress, an expression of negative self-worth, or as a means to gain control over some aspect of suffering.

Development and psychometric properties of the OCD Family Functioning (OFF) Scale.

Obsessive-compulsive disorder (OCD) influences not only patients but also family members. Although the construct of family accommodation has received attention in OCD literature, no measures of overall family functioning are currently available. The OCD Family Functioning (OFF) Scale was developed to explore the context, extent, and perspectives of functional impairment in families affected by OCD. It is a three-part, self-report measure capturing independent perspectives of patients and relatives. A total of 400 subjects were enrolled between 2008 and 2010 from specialized OCD clinics and OCD research studies. Psychometric properties of this scale were examined including internal consistency, test-retest reliability, convergent and divergent validity, and exploratory factor analyses. Both patient and relative versions of the OFF Scale demonstrated excellent internal consistency (Cronbach's alpha coefficient = 0.96). The test-retest reliability was also adequate (ICC = 0.80). Factor analyses determined that the OFF Scale comprises a family functioning impairment factor and four OCD symptom factors that were consistent with previously reported OCD symptom dimension studies. The OFF Scale demonstrated excellent convergent validity with the Family Accommodation Scale and the Work and Social Adjustment Scale. Information gathered regarding emotional impact and family role-specific impairment was novel and not captured by other examined scales. The OFF Scale is a reliable and valid instrument for the clinical and research assessment of family functioning in pediatric and adult OCD. This will facilitate the exploration of family functioning impairment as a potential risk factor, as a moderator and as a treatment outcome measure in OCD.

Cognitive inflexibility and frontal-cortical activation in pediatric obsessive-compulsive disorder.

OBJECTIVE: Deficits in cognitive flexibility and response inhibition have been linked to perturbations in cortico-striatal-thalamic circuitry in adult obsessive-compulsive disorder (OCD). Although similar cognitive deficits have been identified in pediatric OCD, few neuroimaging studies have been conducted to examine its neural correlates in the developing brain. In this study, we tested hypotheses regarding group differences in the behavioral and neural correlates of cognitive flexibility in a pediatric OCD and a healthy comparison (HC) sample. METHOD: In this functional magnetic resonance imaging (fMRI) study, a pediatric sample of 10- to 17-year-old subjects, 15 with OCD and 20 HC, completed a set-shifting task. The task, requiring an extradimensional shift to identify a target, examines cognitive flexibility. Within each block, the dimension (color or shape) that identified the target either alternated (i.e., mixed) or remained unchanged (i.e., repeated). RESULTS: Compared with the HC group, the OCD group tended to be slower to respond to trials within mixed blocks. Compared with the HC group, the OCD group exhibited less left inferior frontal gyrus/BA47 activation in the set-shifting contrast (i.e., HC > OCD, mixed versus repeated); only the HC group exhibited significant activation in this region. The correlation between set shifting-induced right caudate activation and shift cost (i.e., reaction time differential in response to mixed versus repeated trials) was significantly different between HC and OCD groups, in that we found a positive correlation in HC and a negative correlation in OCD. CONCLUSIONS: In pediatric OCD, less fronto-striatal activation may explain previously identified deficits in shifting cognitive sets.