Neuropsychological dysfunction in adults with early-onset obsessive-compulsive disorder: the search for a cognitive endophenotype

The relationship between cognitive phenotypes of compulsivity and impulsivity and clinical variables in obsessive-compulsive disorder: A systematic review and Meta-analysis

BACKGROUND

This systematic review and meta-analysis explored the relationship between cognitive phenotypes of compulsivity and impulsivity and clinical variables in obsessive-compulsive disorder (OCD).

METHODS

We searched Pubmed, Scopus, Cochrane Library and PsychINFO databases until February 2023 for studies comparing patients with OCD and healthy controls on cognitive tests of compulsivity and impulsivity. The study followed PRISMA guidelines and was pre-registered on PROSPERO (CRD42021299017).

RESULTS

Meta-analyses of 112 studies involving 8313 participants (4289 patients with OCD and 4024 healthy controls) identified significant impairments in compulsivity (g = -0.58, [95%CI -0.68, -0.47]; k = 76) and impulsivity (g = -0.48, [95%CI -0.57, -0.38]; k = 63); no significant difference between impairments. Medication use and comorbid psychiatric disorders were not significantly related to impairments. No associations were revealed with OCD severity, depression/anxiety, or illness duration.

CONCLUSION

Cognitive phenotypes of compulsivity and impulsivity in patients with OCD appear to be orthogonal to clinical variables, including severity of OCD symptomatology. Their clinical impact is poorly understood and may require different clinical assessment tools and interventions.

Predictive associations of executive functions and oppositional defiant problems and obsessive-compulsive problems in preschoolers

Oppositional defiant problems (ODP) and obsessive-compulsive problems (OCP) may co-occur in children, though the way they interact is not known. The aim of the study was to examine longitudinal associations between executive functions at age 3 and ODP, ODP dimensions, and OCP at age 6. The sample consisted of 622 preschoolers (50% were boys) from the general population. Executive functions were assessed by teachers using the Behavior Rating Inventory of Executive Functioning - Preschool version questionnaire when children were 3 years old, and ODP and OCP were informed by parents and teachers at the age of 6 years. Multiple linear regression analyses indicated that higher Inhibit and Emotional Control and lower Shift deficits were associated with higher ODP reported by teachers, while higher Shift but lower Inhibit deficits were related to higher OCP. Moreover, ODP and OCP shared difficulties on the Flexibility Index, which means that the capacity to modulate emotions and behavior according to contextual and environmental demands is compromised in both disorders. The findings inform etiology and prevention, pointing out not only the executive function specificities related to each problem, but also common cognitive challenges related to Flexibility. Young children could benefit from training and programs designed to improve executive function processes at an early age to prevent later behavioral difficulties.

Evidence Accumulation and Neural Correlates of Uncertainty in Obsessive-Compulsive Disorder

BACKGROUND

Decision making is frequently associated with risk taking under uncertainty. Elevated intolerance of uncertainty is suggested to be a critical feature of obsessive-compulsive disorder (OCD). However, impairments of latent constructs of uncertainty processing and its neural correlates remain unclear in OCD.

METHODS

In 83 participants (24 OCD patients treated with capsulotomy, 28 OCD control participants, and 31 healthy control participants), we performed magnetic resonance imaging using a card gambling task in which participants made decisions whether to bet or not that the next card would be larger than the current one. A hierarchical drift diffusion model was used to dissociate speed and amount of evidence accumulated before a decisional threshold (i.e., betting or no betting) was reached.

RESULTS

High uncertainty was characterized by a smaller amount of evidence accumulation (lower thresholds), thus dissociating uncertainty from conflict tasks and highlighting the specificity of this task to test value-based uncertainty. OCD patients exhibited greater caution with poor performance and greater evidence accumulation overall along with slower speed of accumulation, particularly under low uncertainty. Bilateral dorsal anterior cingulate and anterior insula distinguished high- and low-uncertainty decision processes in healthy control participants but not in the OCD groups, indicating impairments in anticipation of differences in outcome variance and salience network activity. There were no behavioral or imaging differences relating to capsulotomy despite improvements in OCD symptoms.

CONCLUSIONS

Our findings highlight greater impairments particularly in more certain trials in the OCD groups along with impaired neural differentiation of high and low uncertainty and suggest uncertainty processing as a trait cognitive endophenotype rather than a state-specific factor.

Decision-making deficits in obsessive-compulsive disorder are associated with abnormality of recency and response consistency parameter in prospect valence learning model

Background

Patients with obsessive-compulsive disorder (OCD) have deficits in decision-making in the Iowa Gambling Task (IGT). However, no study has investigated the parameters of the prospect valence learning (PVL) model in the IGT for OCD.

Aims

This study aimed to investigate deficits in decision-making in OCD using the PVL model and identify whether the parameters of the PVL model were associated with obsessive-compulsive severity.

Methods

Forty-seven medication-free patients with OCD were compared with 47 healthy controls (HCs). Decision-making was measured using the total net and block net scores of the IGT. A PVL model with a decay-reinforcement learning rule (PVL-DecayRI) was used to investigate the parameters of the model. Correlation analysis was conducted between each parameter of the PVL-DecayRL and obsessive-compulsive symptoms.

Results

The total net score of patients with OCD was significantly lower than that of the HCs. The block net scores of the OCD group did not differ across the five blocks, whereas in the HCs, the fifth block net score was significantly higher than the block net scores of the first and second blocks. The values of the recency and response consistency parameters of the PVL-DecayRI in patients with OCD were significantly lower than those in HCs. The recency parameter positively correlated with the Y-BOCS obsessive score. Meanwhile, there was no correlation between consistency parameter values and symptom severity in OCD.

Conclusion

Our detailed analysis of the decision-making deficit in OCD suggests that the most recent outcome has a small influence on the expectancy of prospect valence, as indicated by the lower recency parameter, and is characterized by more impulsive choices, as indicated by the lower consistency parameter.

Similarities and differences in working memory and neurometabolism of obsessive-compulsive disorder and major depressive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) and major depressive disorder (MDD) both showed cognitive impairment, and the altered neurometabolic may associate with cognitive impairment. However, there are limited comparative working memory (WM) and neuroimaging studies on these two disorders. Therefore, we investigated the characteristics of WM and neurometabolic changes in patients with OCD and MDD.

METHODS

A total of 64 unmedicated patients (32 OCD and 32 MDD), and 33 healthy controls (HC) were included to conduct WM assessment comprising Digit Span Test (DST), 2-back task and Stroop Color and Word Test (SCWT). Additionally, all subjects underwent protons magnetic resonance spectroscopy (¹H-MRS) to collect neurometabolic ratios of N-acetyl aspartate (NAA) and choline-containing compounds (Cho) to creatine (Cr) in the prefrontal cortex (PFC) and lentiform nucleus (LN). Finally, differential and correlation analysis were conducted to investigate their characteristics and relationships.

RESULTS

Compared with HC, both OCD and MDD patients exhibited a lower accuracy rate in the 2-back task, and only MDD patients performed worse in DST scores and longer reaction times in SCWT (all p < 0.05). Both OCD and MDD patients had lower NAA/Cr ratios in bilateral PFC (all p < 0.05). And the decreased NAA/Cr ratios in right PFC were positively correlated to DST scores in MDD group (r = 0.518, p = 0.003).

CONCLUSIONS

Both OCD and MDD showed WM impairment and neurometabolic alterations in PFC. Besides, MDD performed more severe and broader WM impairment compared to OCD. Moreover, the dysfunction of PFC may underlie the neural basis of WM impairment in MDD.

Neurocognitive endophenotypes in pediatric OCD probands, their unaffected parents and siblings

BACKGROUND

Limited extant research on neurocognitive endophenotypes in obsessive-compulsive disorder (OCD) show inconsistent results. Limitations of this body of literature include small sample sizes, strict exclusion criteria, lack of objective standard normalized test scores, and significant lack of studies utilizing pediatric probands. This study aimed to address these limitations.

METHODS

A large carefully screened cohort of pediatric OCD (n = 102), their unaffected siblings (n = 78), and parents (n = 164), completed a neuropsychological battery. To compare participants at different ages and developmental stages, standard scores were computed using test norms. Cluster-robust regression with sample size-adjusted sandwich estimates of variance, and interclass correlations were computed. False Discovery Rate procedures were employed to correct for multiplicity.

RESULTS

Probands, siblings and parents demonstrated deficient task performance (Z < -0.5) on the 'number of trials to complete first category' on the Wisconsin Card Sorting Test, and on the Stroop color naming trials. Compared to test norms, the three groups exhibited medium to large effect sizes on these outcome measures. No other meaningful familial trends were found.

CONCLUSIONS

OCD probands, their unaffected siblings and parents exhibited deficiencies in specific subdomains of cognitive flexibility and inhibitory control, namely, initial concept formation and proactive control, which may be valid candidate neurocognitive endophenotypes of OCD. No other meaningful familial effect has been found on other functions, including other executive function indices such as perseverations and interference control. These results highlight the need to carefully examine individual outcomes from executive function tests instead of the tendency to focus largely on major outcome measures.

Executive functions and insight in OCD: a comparative study

BACKGROUND

Around 25 to 30% of patients with obsessive-compulsive disorder (OCD) do not respond to treatment. These patients have the longest duration of disease and the worst prognosis. Following years of research on this topic, insight has emerged as a potential explanation for this therapeutic resistance. Therefore, it has become important to characterize OCD patients with poor insight. Few studies have focused on the neuropsychological and cognitive characteristics of these patients.

METHODS

To help fill this gap, we divided 57 patients into two groups, one with good insight and the other with poor insight, assessed their neuropsychological functions-through a Rey's figure test, a California verbal learning test, a Toulouse-Piéron test and a Wisconsin Card Sorting Test (WCST)-and compared the results with those of a paired control group.

RESULTS

The statistical analysis, with a significance level of 95%, revealed differences in the executive function tests, and particularly in the WCST (p ≤ 0.001) and trail-making-test (TMT A/B) (p = 0.002).

CONCLUSIONS

These differences suggest that the neuropsychological profile of poor-insight patients is different from their good-insight counterparts, emphasize the role played by the executive functions in insight and highlights the need for more accurate neurocognitive research and treatment.

Early onset obsessive-compulsive disorder: the biological and clinical phenotype

Moving from a behavioral-based to a biological-based classification of mental disorders is a crucial step toward a precision-medicine approach in psychiatry. In the last decade, a big effort has been made in order to stratify genetic, immunological, neurobiological, cognitive, and clinical profiles of patients. Making the case of obsessive-compulsive disorder (OCD), a lot have been made in this direction. Indeed, while the Diagnostic and Statistical Manual of Mental Disorders (DSM) diagnosis of OCD aimed to delineate a homogeneous group of patients, it is now clear that OCD is instead an heterogeneous disorders both in terms of neural networks, immunological, genetic, and clinical profiles. In this view, a convergent amount of literature, in the last years, indicated that OCD patients with an early age at onset seem to have a specific clinical and biological profile, suggesting it as a neurodevelopmental disorder. Also, these patients tend to have a worse outcome respect to adult-onset patients and there is growing evidence that early-interventions could potentially improve their prognosis. Therefore, the aim of the present paper is to review the current available genetic, immunological, neurobiological, cognitive, and clinical data in favor of a more biologically precise subtype of OCD: the early-onset subtype. We also briefly resume current available recommendations for the clinical management of this specific population.

Obsessive-Compulsive Disorder and Decision Making under Ambiguity: A Systematic Review with Meta-Analysis

In the last decade, decision-making has been proposed to have a central role in obsessive-compulsive disorder (OCD) aetiology, since patients show pathological doubt and an apparent inability to make decisions. Here, we aimed to comprehensively review decision making under ambiguity, as measured by the Iowa Gambling Task (IGT), in OCD, using a meta-analytic approach. According to PRISMA Guidelines, we selected 26 studies for a systematic review and, amongst them, 16 studies were included in a meta-analysis, comprising a total of 846 OCD patients and 763 healthy controls (HC). Our results show that OCD patients perform significantly lower than HC at the IGT, pointing towards the direction of a decision making impairment. In particular, this deficit seems to emerge mainly in the last three blocks of the IGT. IGT scores in OCD patients under the age of 18 were still significantly lower than in HC. Finally, no difference emerged between medicated and unmedicated patients, since they both scored significantly lower at the IGT compared to HC. In conclusion, our results are in line with the hypothesis according to which decision making impairment might represent a potential endophenotype lying between the clinical manifestation of OCD and its neurobiological aetiology.

Neurocognitive Endophenotypes of OCD

In this chapter, I address the concept of endophenotypes for obsessive-compulsive disorder (OCD). Endophenotypes are objective and heritable quantitative traits hypothesized to be more biologically tractable than distal clinical phenotypes. This approach has been adopted to gain a better understanding of psychiatric conditions in general. It is theorized that endophenotypes will particularly assist in clarifying both the diagnostic status and aetiological origins of complex neuropsychiatric conditions such as OCD. At the cognitive level, separable constructs of relevance for OCD have been identified. The prevailing model for OCD assumes the development of abnormalities within fronto-striatal neural circuits leading to impairment of executive functions and their neuropsychological subcomponents. Here, I address whether this model can guide towards the identification of endophenotypes for this condition and discuss possible implications.

Cognitive performance in children and adolescents at high-risk for obsessive-compulsive disorder

BACKGROUND

Cognitive performance has been studied in adults with obsessive-compulsive symptoms (OCS) and in adult relatives of patients with obsessive-compulsive disorder (OCD) Meanwhile, few studies have been conducted with children under the same conditions. This study compared the neurocognitive domains previously associated with dysfunction in OCD, especially visuoconstructive ability, visuospatial memory, executive functions, and intelligence, in children and adolescents at high risk (HR) for OCD (n = 18) and non-OCD controls (NOC) (n = 31).

METHODS

For the HR group, we considered the first-degree relatives of patients with OCD that present OCS, but do not meet diagnostic criteria for OCD. Psychiatric diagnosis was assessed by experienced clinicians using the Structured Clinical Interview for DSM-IV and OCS severity was measured by the Yale-Brown Obsessive-Compulsive Scale. Neurocognitive assessment was performed with a comprehensive neuropsychological battery. Performance on the cognitive domains was compared between groups using Multivariate Analysis of Variance, whereas performance on the neuropsychological variables was compared between groups using independent t-tests in a cognitive subdomain analysis.

RESULTS

The cognitive domain analysis revealed a trend towards significance for impairments in the motor and processing speed domain (p = 0.019; F = 3.12) in the HR group. Moreover, the cognitive subdomain analysis identified a statistically significant underperformance in spatial working memory in the HR group when compared to the NOC group (p = 0.005; t = - 2.94), and a trend towards significance for impairments in non-verbal memory and visuoconstructive tasks in the HR group.

CONCLUSIONS

Our results suggest impairments in spatial working memory and motor and processing speed in a non-clinical sample of HR participants. Considering the preliminary nature of our findings, further studies investigating these neurocognitive domains as potential predictors of pediatric OCD are warranted.

Impairment in the goal-directed corticostriatal learning system as a biomarker for obsessive-compulsive disorder

BACKGROUND

Compulsive behaviors in obsessive-compulsive disorder (OCD) have been related to impairment within the associative cortical-striatal system connecting the caudate and prefrontal cortex that underlies consciously-controlled goal-directed learning and behavior. However, little is known whether this impairment may serve as a biomarker for vulnerability to OCD.

METHODS

Using resting-state functional magnetic resonance imaging (fMRI), we employed Granger causality analysis (GCA) to measure effective connectivity (EC) in previously validated striatal sub-regions, including the caudate, putamen, and the nucleus accumbens, in 35 OCD patients, 35 unaffected first-degree relatives and 35 matched healthy controls.

RESULTS

Both OCD patients and their first-degree relatives showed greater EC than controls between the left caudate and the orbital frontal cortex (OFC). Both OCD patients and their first-degree relatives showed lower EC than controls between the left caudate and lateral prefrontal cortex. These results are consistent with findings from task-related fMRI studies which found impairment in the goal-directed system in OCD patients.

CONCLUSIONS

The same changes in EC were present in both OCD patients and their unaffected first-degree relatives suggest that impairment in the goal-directed learning system may be a biomarker for OCD.

Meta-analysis of neurocognitive deficits in unaffected relatives of obsessive-compulsive disorder (OCD): comparison with healthy controls and patients with OCD

BACKGROUND

Obsessive-compulsive disorder (OCD) has been associated with cognitive deficits, particularly with executive functions. These findings support fronto-striatal dysfunction in OCD. However, it is not certain whether these findings are trait features of OCD. In recent years, a number of studies have investigated cognitive functions in unaffected relatives of OCD (OCDrel) but the findings of these studies are contradictory.

METHODS

A systematic review in Pubmed and Scopus databases was performed until 18 March 2019, to locate the studies comparing cognitive functions of OCDrel with healthy controls and OCD patients (OCDpt). A random-effects meta-analysis was conducted.

RESULTS

Current meta-analysis included 16 studies including 527 OCDrel, 445 OCDpt and 639 healthy controls. Healthy controls overperformed OCDpt in all cognitive domains (d = 0.36-0.86). OCDrel underperformed healthy controls in inhibition (d = 0.58, CI = 0.29-0.86), planning (d = 0.45, CI = 0.28-0.63), decision-making (d = 0.58, CI = 0.19-0.98). OCDrel also had small-sized deficits in set-shifting (d = 0.37, CI = 0.04-0.69) and visual memory (d = 0.28, CI = 0.08-0.49). OCDpt underperformed OCDrel in visual memory (d = 0.45, CI = 0.22-0.67) and set-shifting (d = 0.23, CI = 0.04-0.42).

CONCLUSIONS

Current findings suggest that abnormalities in inhibition, planning/problem solving and reward-based decision-making are shared features of OCDrel and OCDpt and might be trait markers related to vulnerability for developing OCD. Visual memory and set-shifting deficits might potentially be biomarkers of incipient illness or subthreshold OCD presentation among OCDrel. Further exploration of cognitive heterogeneity in OCDrel and investigating the effects of the subtypes of OCD in probands on cognitive impairment in OCDrel are needed.

Endophenotypes of executive functions in obsessive compulsive disorder? A meta-analysis in unaffected relatives

Endophenotypes are mediator traits between genetic influences and clinical phenotypes. Meta-analyses have consistently shown modest impairments of executive functioning in obsessive compulsive disorder (OCD) patients compared to healthy controls. Similar deficits have also been reported in unaffected relatives of OCD patients, but have not been quantified. We conducted the first meta-analysis combining all studies investigating executive functioning in unaffected relatives of individuals with OCD to quantify any deficits. A search of Pubmed, Medline and PsychInfo databases identified 21 suitable papers comprising 707 unaffected relatives of OCD patients and 842 healthy controls. Effect sizes were calculated using random effects models. Unaffected relatives displayed a significant impairment in global executive functioning. Analyses of specific executive functioning subdomains revealed impairments in: planning, visuospatial working memory and verbal fluency. Deficits in executive functioning are promising endophenotypes for OCD. To identify further biomarkers of disease risk/resilience in OCD, we suggest examining specific executive functioning domains.

Abnormal Anhedonia as a Potential Endophenotype in Obsessive-Compulsive Disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) is often accompanied by cognitive, particularly executive function, impairments. Recently, anhedonia has emerged as an apparently important symptom of OCD reflecting altered emotion regulation. These two aspects are often comorbid in OCD. However, little is known about whether anhedonia may be a trait marker for OCD.

METHODS

To verify the role of executive function and evaluate the role of anhedonia in OCD and its relationship with OCD symptoms, we recruited 60 OCD patients, 30 unaffected first-degree relatives (FDRs), and 60 healthy controls (HCs). Participants completed psychometric testing to assess depression, anxiety, and anhedonia symptoms, as well as two cognitive tests to assess executive function, namely the Wisconsin Card Sorting Test (WCST) and the Stroop Color-Word Test (SCWT).

RESULTS

Compared to HCs, OCD patients and FDRs had significantly lower anticipatory and consummatory pleasure scores. The severity of anticipatory anhedonia correlated positively with obsessive-compulsive symptoms (r = 0.253, p = 0.009), even after controlling for depression and anxiety symptoms. Compared to HCs, OCD patients and FDRs made more errors and achieved fewer categories in the WCST. For all three SWCT components, OCD patients and FDRs took more time to name colors than HCs, but the three groups had similar numbers of errors.

CONCLUSION

This family-based study showed dampened pleasure together with cognitive dysfunction in OCD patients. The similar consummatory pleasure findings between OCD and FDR groups suggest anhedonia may be considered as a candidate OCD endophenotype.

Are candidate neurocognitive endophenotypes of OCD present in paediatric patients? A systematic review

To-date it has been difficult to ascertain the exact cognitive profile of childhood OCD as studies report variable results. Adult OCD research lately utilises the endophenotype approach; studying cognitive traits that are present in both patients and their unaffected first-degree relatives, and are thought to lie closer to the genotype than the full-blown disorder. By observing whether candidate endopenotypes of adult OCD are present in child patients, we can determine whether the two subtypes show cognitive overlap. We conducted a systematic review of the paediatric OCD literature focussing on proposed neurocognitive endophenotypes of OCD: cognitive flexibility, response inhibition, memory, planning, decision-making, action monitoring, and reversal learning. We found that paediatric patients present robust increases in brain error related negativity associated with abnormal action monitoring, impaired decision-making under uncertainty, planning, and visual working memory, but there is less evidence for deficits in other cognitive domains. This implies that children with OCD show some cognitive similarities with adult patients, but other dysfunctions may only manifest later in the disorder trajectory.

Executive functions, selective attention and information processing in patients with obsessive compulsive disorder: A study from west of Iran

Obsessive-compulsive disorder (OCD) is associated with cognitive dysfunction. Deeper and wider knowledge of the cognitive components of these patients can play an important role in better understanding of this disorder. This study aimed to compare executive function, selective attention and information processing in OCD patients and healthy controls. The current study was performed on 54 patients meeting DSM-5 criteria for OCD and 54 healthy subjects who matched with patients in gender, age, marital and educational status. The cognitive functions were assessed by The Stroop test, Wisconsin Cart Sorting Test (WCST), Paced Auditory Serial Addition Test (PASAT) and the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). The performance of the OCD group was significantly worse than the healthy group in comparison with the all subscales of the Stroop and WSCT tests. Also, functions in information processing among two groups were statistically significant for 3- and 2-second PASAT. The results demonstrated that OCD patients have deficits in several aspects of cognitive functions. Hence, the treatment of these patients can be contributed by paying more attention to these deficits.

Impaired planning in patients with obsessive-compulsive disorder and unaffected first-degree relatives: Evidence for a cognitive endophenotype

Patients with obsessive-compulsive disorder (OCD) show deficient planning capacity in the Tower of London (TOL) problem solving task. Preliminary evidence for similar deficits in unaffected first-degree relatives suggests that impaired planning may constitute an endophenotype of OCD. However, results on this issue are inconsistent, possibly owing to small sample sizes and variability in problem structure across TOL tasks. Here, we adopted a computerized version of the TOL task featuring a 2 × 2 factorial design (high/low search depth × full/partial tower goal state) and examined a well-characterized sample of n = 72 OCD patients, n = 76 unaffected first-degree relatives and n = 102 healthy comparison subjects. Both OCD patients and relatives exhibited significantly less accurate problem solving than controls. Search depth, goal hierarchy, or the number of minimum moves did not moderate these group differences. Medication, OCD symptoms, and depressive comorbidity did not affect TOL performance in patients, suggesting a state-independent effect. In conclusion, we found that OCD patients as well as unaffected first-degree relatives show deficient TOL performance across a range of task conditions, strongly supporting the role of impaired planning as an endophenotype of OCD, and contributing to the growing evidence for fronto-striatal dysfunctions in OCD.

The Flexibility Scale: Development and Preliminary Validation of a Cognitive Flexibility Measure in Children with Autism Spectrum Disorders

Flexibility is a key component of executive function, and is related to everyday functioning and adult outcomes. However, existing informant reports do not densely sample cognitive aspects of flexibility; the Flexibility Scale (FS) was developed to address this gap. This study investigates the validity of the FS in 221 youth with ASD and 57 typically developing children. Exploratory factor analysis indicates a five-factor scale: Routines/rituals, transitions/change, special interests, social flexibility, and generativity. The FS demonstrated convergent and divergent validity with comparative domains of function in other measures, save for the Generativity factor. The FS discriminated participants with ASD and controls. Thus, this study suggests the FS may be a viable, comprehensive measure of flexibility in everyday settings.

Rodent models of obsessive compulsive disorder: Evaluating validity to interpret emerging neurobiology

Obsessive Compulsive Disorder (OCD) is a common neuropsychiatric disorder with unknown molecular underpinnings. Identification of genetic and non-genetic risk factors has largely been elusive, primarily because of a lack of power. In contrast, neuroimaging has consistently implicated the cortico-striatal-thalamo-cortical circuits in OCD. Pharmacological treatment studies also show specificity, with consistent response of OCD symptoms to chronic treatment with serotonin reuptake inhibitors; although most patients are left with residual impairment. In theory, animal models could provide a bridge from the neuroimaging and pharmacology data to an understanding of pathophysiology at the cellular and molecular level. Several mouse models have been proposed using genetic, immunological, pharmacological, and optogenetic tools. These experimental model systems allow testing of hypotheses about the origins of compulsive behavior. Several models have generated behavior that appears compulsive-like, particularly excessive grooming, and some have demonstrated response to chronic serotonin reuptake inhibitors, establishing both face validity and predictive validity. Construct validity is more difficult to establish in the context of a limited understanding of OCD risk factors. Our current models may help us to dissect the circuits and molecular pathways that can elicit OCD-relevant behavior in rodents. We can hope that this growing understanding, coupled with developing technology, will prepare us when robust OCD risk factors are better understood.

Cognitive Dysfunction in Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a mental disorder featuring obsessions (intrusive thoughts) and compulsions (repetitive behaviors performed in the context of rigid rituals). There is strong evidence for a neurobiological basis of this disorder, involving limbic cortical regions and related basal ganglion areas. However, more research is needed to lift the veil on the precise nature of that involvement and the way it drives the clinical expression of OCD. Altered cognitive functions may underlie the symptoms and thus draw a link between the clinical expression of the disorder and its neurobiological etiology. Our extensive review demonstrates that OCD patients do present a broad range of neuropsychological dysfunctions across all cognitive domains (memory, attention, flexibility, inhibition, verbal fluency, planning, decision-making), but some methodological issues temper this observation. Thus, future research should have a more integrative approach to cognitive functioning, gathering contributions of both experimental psychology and more fundamental neurosciences.

Effects of stress on behavioral flexibility in rodents

Cognitive flexibility is the ability to switch between different rules or concepts and behavioral flexibility is the overt physical manifestation of these shifts. Behavioral flexibility is essential for adaptive responses and commonly measured by reversal learning and set-shifting performance in rodents. Both tasks have demonstrated vulnerability to stress with effects dependent upon stressor type and number of repetitions. This review compares the effects of stress on reversal learning and set-shifting to provide insight into the differential effect of stress on cognition. Acute and short-term repetition of stress appears to facilitate reversal learning whereas the longer term repetition of stress impairs reversal learning. Stress facilitated intradimensional set-shifting within a single, short-term stress protocol but otherwise generally impaired set-shifting performance in acute and repeated stress paradigms. Chronic unpredictable stress impairs reversal learning and set-shifting whereas repeated cold intermittent stress selectively impairs reversal learning and has no effect on set-shifting. In considering the mechanisms underlying the effects of stress on behavioral flexibility, pharmacological manipulations performed in conjunction with stress are also reviewed. Blocking corticosterone receptors does not affect the facilitation of reversal learning following acute stress but the prevention of corticosterone synthesis rescues repeated stress-induced set-shifting impairment. Enhancing post-synaptic norepinephrine function, serotonin availability, and dopamine receptor activation rescues and/or prevents behavioral flexibility performance following stress. While this review highlights a lack of a standardization of stress paradigms, some consistent effects are apparent. Future studies are necessary to specify the mechanisms underlying the stress-induced impairments of behavioral flexibility, which will aid in alleviating these symptoms in patients with some psychiatric disorders.