Extended Abstract
1. Introduction
Obsessive-Compulsive Disorder (OCD) is characterized by the world health organization as a major cause of mental disturbance. Biological approach is one of the viewpoints in the field of etiology of psychological disorders, especially the OCD. In this regard, Gray and McNaughton’s reinforcement sensitivity theory is one of the most important theories investigating the biological basis of psychological disorders and personality. Based on this theory, Gray [6] raised the notion that psychiatric disorders are the result of a dysfunction, either in brain-Behavioral Activation System (BAS) or in brain-Behavioral Inhibition System (BIS). Losing the interaction between the two systems can also result in a similar outcome. 
Although there are definite direct relationships between BAS sensitivity, BIS sensitivity, and mental disorders, evidence suggests that these direct relationships can only be a partial explanation for these relationships. Hence, intermediary mechanisms such as disgust sensitivity have been proposed for a better understanding of the relationship between brain-behavioral systems and OCD. Disgust as a negative and inclusive emotion involves a feeling of intense hatred and reluctance, which encompasses different physiological, cognitive, and behavioral dimensions. Given the fact that previous research directly investigated the relationships between these variables, the more important issue is to rearrange these variables in a more structured model that can accurately explain the relationships between these variables. Therefore, the purpose of this study was to test the structural relationships between brain-behavioral systems, disgust sensitivity, and OCD.
2. Method
The present study is a fundamental type and of a descriptive-correlational type in terms of data collection. Considering the minimum sample size required when the variables of the model (in the hypothesized model of the present study, 15 variables) ranges from 10 to 15, the sample size should be between 200 and 400 [21]. Therefore, the sample size of this study was equal to 340 subjects. To choose the subjects, firstly, using a cluster sampling method, four colleges (including human sciences, technical, basic sciences and agriculture) were randomly selected. Then from each college, a number of students were randomly selected to include them in the research. To test the research hypotheses, the collected data were analyzed using SPSS 22 and LISREL 8.85 software. [28]. The fitness of the hypothesized model was assessed using the Structural Equation Modeling (SEM) method. The data analysis was performed using the two-step approach of Anderson & Gerbing [29] as follows: in the first step, Confirmatory Factor Analysis (CFA) was used to assess the fitness of the measurement model, and in the second step, SEM was employed to assess the hypothesized structural model.
3. Results 
The matrix of correlation coefficients between the variables of the research is shown in Table 1. As the content of the table shows, the correlations are significant (-0.697≥r≥0.611). The measurement model specifies the relationship between the observed and latent variables. The evaluation of the model was done using CFA method. The fit indices of the measurement model (Table 2) show a satisfactory fitness for this model. Therefore, the observed variables are capable of operating the latent variables.
In addition, assessing the structural model via the SEM method revealed that all the fit indices of the hypothesized model were within the appropriate fitness range. The fit indices for this model are shown in Table 2. Figure 1 depicts the hypothetical structural model with its standard coefficients. As can be seen from Figure 1, the brain-Behavioral Activation System (BAS) and the brain-Behavioral Inhibition System (BIS) as exogenous variables have an effect on the disgust sensitivity with a standard coefficient of -0.36 and -0.39, respectively. In addition, disgust sensitivity affects OCD with a standard coefficient of 0.67.
In the current study, the Bootstrap test was employed to evaluate the intermediate relationships. In this method, 

 

if the upper and lower limits of this test are either positive or negative, and zero is not between these two limits, then the indirect causal path will be significant. Table 3 presents the results of this test.
4. Discussion
The present study, using a hypothetical structural model, tested the relationships between OCD, BIS and BAS, while the mediating role of disgust sensitivity was taken into account. As assumed, the findings supported a model in which the high BIS sensitivity and the low BAS sensitivity, due to the mediating role of disgust sensitivity, led to an escalation in the symptoms of OCD. The findings of this study signified that BIS and BAS as two biological traits of personality, with a mediating role of disgust sensitivity, have positive and negative effects, respectively on symptoms of OCD. In accordance with the findings of this study, research evidence suggests that BIS and BAS which show themselves as emotional styles are a major risk factor for emotional disturbances. Moreover, the unusual sensitivity of these systems provides readiness and vulnerability against the various kinds of psychiatric pathology [7] so that BAS and BIS can explain a wide range of disorders. 
Olatunji et al. (2015) [15], who investigated the relationships between several personality factors and disgust, showed that the BIS is strongly correlated with disgust. Researchers believe that the relationship between BIS and disgust indicates that disgust usually serves as a regulator for aversive motivations. In particular, as disgust is usually associated with a negative stimulus, and since the BIS acts as an independent functional system that regulates behavior and motivation in response to annoying situations, the BIS’s sense of disgust may serve as a warning against the occurring upcoming punishment. In other words, disgust is considered a negative and annoying event, which is subsequently used by the BIS to respond to and regulate future behaviors and motivations.
Acknowledgements
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of Interest
The authors declare no conflicts of interest.
 

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