دو نوع اختلال در OCD: وسواس فکری، به عنوان مشکلات سرکوب افکار. رفتارهای اجباری به عنوان اختلال رفتاری اجرایی

Impairments in executive functioning have been identified as an underlying cause of Obsessive-Compulsive Disorder (OCD). Obsessive patients attempt to suppress certain unwanted thoughts through a mechanism that Wegner referred to as ‘chronic thought suppression’, whereas compulsive patients are unable to inhibit their rituals. We tested 51 OCD patients using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS), the White Bear Suppression Inventory (WBSI) and the Dysexecutive Questionnaire (DEX). Executive functions were tested using a cognitive test battery. We found that the total WBSI score was correlated with the Y-BOCS obsessive score but not with the Y-BOCS compulsive score. A stronger correlation was observed between the Y-BOCS obsessive score and the ‘unwanted intrusive thoughts’ factor based on Blumberg's 3-factor model of the WBSI. The total WBSI score was not correlated with the cognitive test results. The DEX score was significantly correlated with the Y-BOCS compulsive score; however, no correlation was found between the DEX score and the Y-BOCS obsessive score. A stronger correlation was observed between the Y-BOCS compulsive score and the ‘inhibition’ component of the DEX score, as defined by Burgess's 5-factor model. The DEX scores were correlated with cognitive test results measuring attention, cognitive flexibility and inhibitory processes. We conclude that obsessions indicate a failure of cognitive inhibition but do not involve significant impairment of executive functions, whereas compulsions indicate ineffective behavior inhibition and impaired executive functions.

Obsessions and compulsions are characteristic symptoms of Obsessive-Compulsive Disorder (OCD). Obsessions are intrusive, unwanted thoughts or images that patients are unable to ignore or block. Additionally, OCD patients tend to perform compulsions, which are perseverative behaviors or rituals that they are unable to interrupt or stop. Executive dysfunction is assumed to underlie both symptoms (Kuelz et al., 2004). 1.1. The dysexecutive syndrome and the Dysexecutive Questionnaire (DEX) Adequate frontal lobe functioning is necessary for efficient executive functioning. According to Norman et al's. (2000) classification, executive functions are required in situations where routine activation of behavior would not be sufficient for optimal performance . The significance of failure of inhibitory functions in dysexecutive syndrome was proposed by several research groups beginning in the early 1980s (Shimura, 1995 and Burgess, 1997). Prior research has revealed that dysexecutive symptoms can be identified not only in patients with brain injury, but also in those with psychiatric diseases like schizophrenia, depression and OCD (Evans et al., 1997, Tibbo and Warneke, 1999 and Cavanagh et al., 2002). Several validated cognitive tests and questionnaires are available to assess frontal lobe functioning, together with Behavioral Assessment of the Dysexecutive Syndrome (BADS) which is a cognitive test battery that includes the DEX questionnaire. The DEX is a standardized instrument to measure behavioral changes as a result of dysexecutive syndrome. The DEX measures dysexecutive symptoms at the behavioral level and is particularly designed to assess errors in goal-directed behaviors that occur during everyday life (Burgess et al., 1998). Several research groups have attempted to identify different factors of the DEX through factor analysis (Burgess et al., 1998, Chan, 2001, Amieva et al., 2003, Chaytor et al., 2006 and Pedrero-Perez et al., 2009). Although researchers have identified different factors (or dimensions) of the DEX, one common factor can be identified in all dimensional approaches, namely, the impairment of inhibitory functions. The BADS/DEX test battery proved to be valid not only in patients with brain injuries but also in patients with psychiatric diseases such as schizophrenia (Evans et al., 1997), schizotype personality disorder (Laws et al., 2008), bipolar affective disorder (Cavanagh et al., 2002) and Asperger syndrome (Cederlund et al., 2010). To the best of our knowledge, however, the DEX questionnaire has not yet been used to study the dysexecutive symptoms in OCD. 1.2. The failures of cognitive and behavioral inhibitory processes in OCD The failure of inhibitory processes has been theorized to occur in OCD by many researchers, although the term ‘inhibition’ has been used to signify various different features of distinct aspects of OCD (see Table 1). Chamberlain et al. (2005) emphasized the importance of failures of cognitive and behavioral inhibitory processes in OCD. These researchers identified two different failures of inhibitory processes in OCD, namely, a failure of cognitive inhibition that primarily relates to obsessive symptoms and a failure in behavior inhibition that is linked to compulsions. The authors hypothesize that these two failures in inhibitory processes are associated with distinct neural pathways and different cognitive dysfunctions. In a subsequent study, Chamberlain et al. (2006) specifically investigated the dysfunction of motor inhibitory control and cognitive flexibility, as this dysfunction has been theorized to be a central characteristic of OCD. Executive motor inhibition impairment can be measured by cognitive assessments, such as the Go/No-go Task, the Stroop Test and the Stop Signal Task. According to the psychometric analysis of Friedman and Miyake (2004), the Stroop test and the Stop Signal Task utilize the same component of the executive inhibitory control system, namely, prepotent response inhibition. The failure of executive cognitive flexibility is correlated with attentional set-shifting disturbance, which can be detected with assessments such as the Wisconsin Card Sorting Test (WCST), the Trial Making Test (TMT), or the Intradimensional/Extradimensional Shift Task (Kuelz et al., 2004 and Chamberlain et al., 2006). Chamberlain et al. (2006) investigated motor inhibition using the Stop Signal Task and evaluated cognitive flexibility using the Intradimensional/Extradimensional Shift Task. Impairments in the intentional inhibition of simple motor actions have been demonstrated in OCD patients. Moreover, the impaired inhibition of simple motor responses has also been detected in unaffected first-degree relatives of OCD patients (Chamberlain et al., 2007), which has led to the proposal that response inhibition deficits may provide a useful intermediate marker of brain dysfunction, that is, that these deficits could represent an endophenotype for OCD. Recently, Morein-Zamir et al. (2010) used the Thought Stop Signal Task (TSST) to investigate whether the impaired stopping/suppression observed in OCD patients could extend to the inhibition of ongoing thoughts as well. Table 1. The different aspects of inhibition that are theorized in OCD. Dysexecutive Questionnaire (DEX) (Burgess, 1997) Chamberlain et al. (2005) Chamberlain (2006)/ Morein-Zamir et al. (2010) White Bear Suppression Inventory (WBSI) (Wegner and Zanakos, 1994) Wegner and Zanakos (1994) (Ironic process theory) − The assessment of the dysexecutive symptoms in everyday goal-directed behaviors (behavior level) − Inhibition factor/dimension − Cognitive inhibition impairment (obsessions) − Behavior inhibition impairment (compulsions) − Motor inhibition impairment − Cognitive inflexibility (measured by neurocognitive tests) − Thought intrusions − Cognitive inhibition of unwanted thought: thought suppression − Operating inhibitory processes (conscious) − Monitoring processes (unconscious) Table options 1.3. Wegner's theory of cognitive inhibition of thoughts and thought suppression: the White Bear Suppression Inventory (WBSI) The clinical presentation of OCD has driven researchers to investigate the integrity of controlled memory processes and executive functions in this disorder (Heuvel et al., 2005). Wegner et al. investigated memory inhibition processes using a paradigm in which thought suppression was required, i.e., by instructing participants, ‘Do not think of a white bear!’ (Wegner and Zanakos, 1994). Compared to those who had not used suppression, there was evidence for unwanted thoughts being immediately enhanced during suppression and, furthermore, for a higher frequency of target thoughts during the second stage, called rebound effect (Wegner, 1989). Thought suppression has paradoxical effects because it may cause the suppressed thought to be deeply activated and highly accessible (Wenzlaff and Wegner, 2000). Wegner and Zanakos (1994) theorized that two concurrent systems are triggered when an individual attempts to avoid a particular act or thought. One of these systems is a conscious operating process, which searches for mental content consistent with the intended state until this search is destabilized by distractions. This operating process requires conscious effort, as it is a controlled (non-automatic) process. The other system of Wegner's theory is an implicit monitoring process, which is unconscious and searches for mental content that is inconsistent with the intended state and the achievement of successful control. The operating process requires greater cognitive capacity than the monitoring process. When the operating process is voluntarily terminated, the monitoring process continues its vigilance for unwanted thoughts. This ‘online’ monitoring process increases the mind's sensitivity to unwanted material, a phenomenon that can explain the occurrence of post-suppression rebound and the ironic aspects of thought suppression (Wegner 1994, Wenzlaff and Wegner, 2000). Wegner et al. (1987) concluded that certain individuals frequently use thought suppression as a coping mechanism. These investigators called this cognitive inhibition mechanism ‘chronic thought suppression’ and hypothesized that chronic thought suppression is of outstanding significance in OCD patients. To enable researchers to identify people who are more prone to suppressing thoughts in their daily lives, Wegner and Zanakos (1994) constructed a measure of chronic thought suppression, the White Bear Suppression Inventory (WBSI),which they validated by administering the WBSI to healthy subjects, patients with OCD and patients with depression. The WBSI scores correlated strongly with obsessive scores but were less strongly correlated with compulsive scores. Wegner and Zanakos (1994) thought, that “thought suppression does not predict compulsive behavior because the two are alternative means of coping with unwanted thoughts. It may be too, that engaging in behaviors that are intended to neutralize unwanted thoughts or solve the problems such thought represent somehow undermines the individual's tendency to self-report attempting to suppress those thoughts.” In a subsequent study, Muris et al. (1996) demonstrated that a greater rebound effect of unwanted intrusive thoughts following a thought suppression task was reported by participants with high WBSI scores than by participants with low WBSI scores . Originally, Wegner and Zanakos published the WBSI as a unidimensional construct; however, the test contains questions related to both intrusive thoughts and thought suppression tendencies. The broad scope of the WBSI can simultaneously serve as both an advantage and a disadvantage of this assessment technique. Therefore, to facilitate more detailed analyses of WBSI results, Höping et al. demonstrated that the WBSI can be decomposed into two factors, namely, unwanted intrusive thoughts and thought suppression. By separating thought intrusions from thought suppression, researchers can conduct differential assessments of these constructs, which may prove to be an important aspect of analyzing WBSI results (Höping and Jong-Meyer, 2003). Blumberg (2000) collected WBSI data from 935 healthy subjects to examine the WBSI factor structure and identified the following three WBSI factors: unwanted intrusive thought, thought suppression and self-distraction (see Table 2). Table 2. Blumberg's 3-factor model of the White Bear Suppression Inventory (WBSI). I. Factor: ‘unwanted intrusive thoughts’ 2. Sometimes I wonder why I have the thoughts I do. 3. I have thoughts that I cannot stop. 4. There are images that come to mind that I cannot erase. 5. My thoughts frequently return to one idea. 6. I wish I could stop thinking of certain things. 7. Sometimes my mind races so fast I wish I could stop it. 9. There are thoughts that keep jumping into my head. 15. There are many thoughts that I have that I don’t tell anyone. II. Factor: ‘thought suppression’ 1. There are things I prefer not to think about. 8. I always try to put problems out of mind. 11. There are things that I try not to think about. 14. I have thoughts that I try to avoid. III. Factor: ‘self distracters’ 10. Sometimes I stay busy just to keep thoughts from intruding on my mind. 12. Sometimes I really wish I could stop thinking. 13. I often do things to distract myself from my thoughts. Table options 1.4. Intrusive thoughts and thought suppression in OCD The high rate of recurrence of inhibited (‘censored’) thoughts is of great significance in everyday clinical practice. The majority of the population experiences unwanted thoughts and images occasionally but can dismiss these undesired thoughts as harmless anomalies. By contrast, obsessions are thoughts that give rise to immediate resistance. Active resistance is a crucial feature of obsessions and is an important criterion for distinguishing obsessions from other types of persistent, negative and unwanted thoughts, which can arise from conditions such as depressive rumination or anxiety (Wenzlaff and Wegner, 2000). Thought suppression is an effortful activity that requires attentional resources and may therefore impair an individual's ability to concentrate on performing other tasks (Wegner and Zanakos, 1994). Thought suppression renders an individual hypervigilant to thoughts and thought processes; as a result, thought triggers and thought traces are much more salient than normal for the individual in question and the inevitable thought recurrences that arise during the suppression process exacerbate the negative appraisal of the meanings of these thoughts (Purdon, 2004). Research on thought suppression in OCD has yielded inconsistent findings (Purdon, 2004), but these findings do suggest that thought suppression efforts and their impact may contribute significantly to the severity of impairment associated with OCD; therefore, it may prove useful for clinical and research purposes to evaluate suppression as a potential severity indicator of OCD. (Purdon, 2004 and Magee and Teachman, 2007). However, the existing measures of OCD symptoms and severity (the Padua Inventory, the Obsessive Compulsive Inventory, the Maudsley Obsessional Compulsive Inventory and the Yale-Brown Obsessive Compulsive Scale) do not directly evaluate suppression (Purdon et al., 2007). Therefore, drawing on the ideas of Purdon et al. (2007), we conjecture that the WBSI, which is a validated questionnaire for assessing both intrusive thoughts and thought suppression tendencies, may be a relevant measurement tool for completing the symptom severity scales that are used in OCD. 1.5. Aim of the study In the present study, we defined two OCD subgroups based on the obsessive and compulsive subscores of the Y-BOCS symptom severity scale. For the assessment of cognitive functioning, validated cognitive tests of sustained attention, cognitive flexibility (set-shifting ability) and executive inhibition were used. We did not include any healthy controls in this study, as the present analysis focused on the characteristic differences between the predominantly obsessive and predominantly compulsive subgroups of OCD rather than on the differences between OCD patients and a healthy control group. 1. The aim of this study was to use the WBSI to assess the levels of intrusive thought occurrences and thought suppression tendencies in OCD patients and to use the DEX to evaluate the dysexecutive symptoms of these patients; the results of these questionnaires were related to executive functions in the OCD patients. 2. In the case of obsessions, it has been established that the core failure is ineffective cognitive inhibition (Chamberlain et al., 2005); therefore, we were interested in discovering whether ‘chronic thought suppression’, as measured by the WBSI, is typical of all OCD patients or whether this thought suppression is more apparent in patients with either only obsessive or only compulsive symptoms. Because the WBSI measures both components of thought suppression (namely, intrusive thoughts and thought suppression tendencies), we were particularly interested in Blumberg's dimensional approach, which can separate these two components. We were also interested in elucidating the relationship in OCD patients between thought suppression and executive functions, which were assessed by the aforementioned cognitive tests. In accordance with Wegner's (1994) theory, we hypothesized that obsessive thoughts in OCD are the consequence of an over-activated automatic monitoring system; this monitoring system does not require effortful activity and therefore should not produce a general executive deficit. 3. We theorized that a failure occurs in behavioral-executive inhibitory processes in the case of compulsions (Chamberlain et al., 2005). We were particularly interested in the correlations between the dysexecutive functions measured by the DEX and the Y-BOCS and the obsessive and compulsive subscales. In addition, we wished to discover the correlation between the cognitive test results and the dysexecutive functions measured by the DEX and the 5 individual factors of the DEX (following Burgess's dimensional approach). Because compulsions are conscious, effortful activity, we theorized, in accordance with Wegner's (1994) theory, that compulsions indicate a failure in conscious operating processes, which require significant cognitive capacity. This failure, in turn, leads to relevant impairments in the goal-directed behaviors of everyday life for OCD patients (as measured by the DEX) as well as executive dysfunction (as measured by the cognitive tests).

Descriptive statistics of the 51 OCD patients in the sample are presented in Table 4. The WBSI scores were analyzed using Blumberg's 3-factor model and the DEX scores were analyzed using Burgess's 5-factor model (for details, see Methods). The results are shown in Table 4. Based on the normative scales of the DEX questionnaire the presence and severity of executive problems of our 51 OCD patients were between 31 and 53 percentil, which shows a severe executive impairment comparing to the normal control of the manual of the DEX.