تکانشگری ازادی از اسارت، پرخاشگری و پرخاشگری تکانشی: یک رویکرد تجربی با استفاده از اقدامات خود گزارش دهی

There is confusion in the literature concerning the concept of impulsive aggression. Based on previous research, we hypothesize that impulsivity and aggression may be related, though not as closely as to consider them the same construct. So, our aim was to provide empirical evidence of the relationship between the impulsivity and aggressiveness constructs when considered as traits. Two widely used questionnaires [Barratt's Impulsiveness Scale (BIS) and Aggression Questionnaire—Refined (AQ-R)] were administered to 768 healthy respondents. Product-moment and canonical correlations were then calculated. In addition, a principal components analysis was conducted to explore whether impulsive aggression can be defined phenotypically as the expression of a single trait. The common variance between impulsivity and aggressiveness was never higher than 42%. The principal components analysis reveals that one component is not enough to represent all the variables. In conclusion, our results show that impulsivity and aggressiveness are two separate, although related constructs. This is particularly important in view of the misconceptions in the literature.

According to the World Health Organization, violence is one of the leading public health problems worldwide (Krug et al., 2002). Acts of aggression have a deep impact on society and therefore on psychiatry and related fields. But what is aggression? Many definitions have been put forward. The most widely accepted is the one proposed by Berkowitz (1993): a goal-directed motor behavior that has a deliberate intent to harm or injure another object or person. This is a relatively consensual definition of aggression (Berkowitz and Harmon-Jones, 2004). In order to understand the etiology and origins of aggressive behavior and to find a successful treatment, several taxonomic systems have been proposed (Parrott and Giancola, 2007). However, although there is relative agreement that aggression refers to observable behavior, the terms “anger", “aggression", “hostility", “impulsivity" and other traits and behaviors have been used interchangeably by some clinicians and researchers, while remaining clearly distinct to others (Suris et al., 2004). This lack of clarity may be representative of the theoretical overlap of concepts, or it may be that some terms represent behavioral manifestations of the higher level organizing principles represented by other terms. Some authors (Coccaro, 1998) state that there may be a lack of conceptual differentiation between the terms used to represent target behaviors, which has led to confusion in differentiating between predictor and criterion measures. It is important to define clear criteria to explore the constructs, because precise criteria would improve predictions based on measures of observable conducts or non-observable traits (predictors). Moreover, confusion may arise both at conceptual or methodological levels. It is also evident in the DSM-IV-TR, where there is no specific definition of aggression. In addition, it includes a cluster of underlying and precipitating variables that are frequently related to aggression (Buss and Perry, 1992 and Eysenck and Eysenck, 1978), the most important of them being impulsivity (Hollander and Stein, 1995). Some authors state that these variables are interrelated via higher order constructs to the degree that they share common variance (Suris et al., 2004). Impulsivity is often defined as “a predisposition toward rapid, unplanned reactions to internal or external stimuli without regard to the negative consequences of these reactions to the impulsive individual or to others”, p. 1784 (Moeller et al., 2001), a definition only suitable for a personality trait, understood as a propensity to emit a certain response to stimuli. Considerable efforts have been devoted to the classification of aggressive behaviors. Barratt and Slaughter (1998) classified aggression into three categories: premeditated, medically related, and impulsive. Coccaro went a step further and defined impulsive aggression as aggressive behavior in a deliberate and non-premeditated fashion (Coccaro, 1998 and Moeller et al., 2001). This distinction between premeditated and impulsive aggression has become popular in the literature (Coccaro and Kavoussi, 1997 and New et al., 2002), and has even led to the development of specific tools to capture it (Mathias et al., 2007 and Stanford et al., 2003). Impulsive aggression per se has been described variously as (1) a single trait-like dimension ( Coccaro et al., 1989 and Siever and Davis, 1991); (2) a subset of impulsive behaviors (e.g., “impulsivity with an aggressive flair”: Seroczynski et al., 1999); (3) a subset of aggressive behaviors (e.g., “unplanned aggression”: Barratt et al., 1994 and Barratt et al., 1999); or (4) the combination or interaction of separate traits ( Depue and Lenzenweger, 2001). As a result of this mixture of definitions both in terms of traits and behaviors, boundaries and relations between terms are unclear ( Critchfield et al., 2004, p. 558). For instance, in an excellent review, Coccaro (1992) argues “that the existence of a dimensional brain–behavior relationship such that reduced central 5-HT system function in patients affected by major mood and/or personality disorder is associated with a trait dysregulation of impulse control, the presence of which enhances the likelihood of self- and/or other-directed aggressive behavior, given appropriate environmental triggers” (p. 10). Critchfield et al. (2004) points out that one implication of this theory is that impulsivity and aggression are expected to appear together on the phenotypic level, justifying the use of the term impulsive aggression as a single trait-like dimension. Regarding the assessment of impulsive aggression, Coccaro and his team (Coccaro, 1998 and Coccaro et al., 1998) devoted much effort to defining the concept of intermittent explosive disorder (IED). These articles laid the groundwork for future research in the field and were later on extended to children and adolescents (Olvera et al., 2001). In those seminal articles, Coccaro and colleagues explored the reliability and validity of IED based on behavioral measures. Certainly, it was a cleverly designed study and it provided useful insights on the diagnosis of IED, but it might seem that their results went unnoticed in the literature. When addressing the issue of construct validity (Coccaro et al., 1998), they stated that “the findings using the impulsivity measures were less striking with only a trend towards statistical significance for BIS-11 impulsivity (F[1,56] = 3.70, P = 0.061) and no significant difference on the I7 impulsivity (F[1,62] = 2.05, P = 0.16) measures” (p. 371, the italics added). Coccaro and his group do not view impulsivity and aggression as interchangeable, but they fail to clarify the issue in the discussion by simply pointing out that subjects with IED-R scored higher on impulsivity. Certainly, they scored higher in their sample, but not significantly, which invalidates the argument for the population. These criteria have influenced other studies in the field (e.g. Best et al., 2002), which perpetuate the same misinterpretation: “Severe psychiatric conditions related to IED are characterized by the inability to inhibit aggressive or impulsive behavior” (p. 5, italics added). Nonetheless, there is evidence of a misuse of the term “impulsive aggression". For instance, Dolan et al. (2001) explored the relationships between impulsivity, aggression and serotonin function in a sample of male offenders with personality disorders. They stated that “impulsivity and aggression were difficult to separate”, but they used composites based on z-scores, and, although aggression scores were not significant for prediction of serotonergic function, they refer throughout the article to “impulsivity/aggression” (p. 358). In another study, Siever et al. (1999) studied the d,l-fenfluramine response in “impulsive personality disorder" with positron emission tomography. They equate “impulsive aggression disorder" with “intermittent explosive disorder" assessed by means of the “Module for Impulse Aggression Disorder (E. Coccaro et al., personal communication)" (p. 414, italics added). This kind of misinterpretation should be avoided, the original citation is “Module for Intermittent Explosive Disorder—Revised”. It is easy to get confused only by changing two words. Terminology should be precise; careless use of terms renders them meaningless. This article influenced Dougherty et al. (2004) in the discussion of their results. In that sample, they assessed anger attacks by means of a questionnaire specifically designed with this aim ( Fava et al., 1991), but they assess neither impulsivity nor aggressiveness psychometrically as a trait. However, in the discussion, they state (p. 801) that these studies provide evidence about the pathophysiology of impulsive aggression without providing any definition for it. In an excellent and influential review, Moeller et al. (2001) addressed some key features of impulsivity and its relation to psychiatric disorders. They cover core aspects of impulsivity very well, but they conclude their article by stating (p. 1790) that “aggressive acts are more easily measured than other aspects of impulsivity”. We agree with Moeller et al. (2001) that capturing core aspects is necessary, but, again, we must distinguish between acts (or observable behavior, e.g. an aggression) and traits or predispositions (e.g. impulsivity), which are non-observable, inferred constructs. They are at different levels of analysis. Positron emission tomography has been also related to “impulsive aggression” (New et al., 2002). The authors selected patients “who met DSM-IV criteria for 1 or more personality disorders” (p. 622) and with regard to measures, “trait aggression was assessed using the Module for Intermittent Explosive Disorder—Revised” (p. 622). In this case, specificity of the findings within the framework of impulsive aggression is difficult to attain, given comorbidity rates among personality disorders. Moreover, the Module for Intermittent Explosive Disorder was not designed to assess trait aggression. Throughout the article, the authors did not use any single test to measure impulsivity. The contribution of this article to the neurobiology of aggression is relevant, but impulsivity is neither assessed nor mentioned in the discussion. More importantly, in this study actual aggression was not measured, but aggressiveness. Again, there is confusion when referring to aggression, aggressiveness, impulsive aggression or an impulse. Frankle et al. (2005) used a composite index of impulsive aggression based on a few clinical items (p. 916). This article has received 24 citations since publication as it provides good contributions, but it is remarkable how carefully prepared is the neuroimaging paradigm, and how comparatively little attention they paid to behavioral assessment. Moreover, they refer to impulsive aggression while using the term “impulsive aggressivity" in the title. These are just a few examples of the lack of clarity in the field. Impulsivity as a sign, and also as a symptom, cuts across a number of psychiatric disorders (Moeller et al., 2001), and it is a feasible endophenotype for many disorders (Gould and Gottesman, 2006). As presented before, some researchers say “aggression" when they refer to “aggressiveness", some say “impulsive aggression" when they simply want to say “aggression", and so on. This is a matter of concern, since it affects the definition and operationalization of the descriptor “impulsive." The lack of scientific rigor that this entails may lead to errors in the interpretation of research results from a theoretical point of view. What are the reasons leading to confusion? They could be summarized as follows: (a) definitions of impulsivity are rather similar to those of aggressiveness or aggression (Berkowitz, 1993 and Moeller et al., 2001); one could argue that this similarity between definitions could be a focus of confusion and could lead to invalid operationalization of these variables. (b) Another explanation that might underlie the confusion is the misunderstanding of what is a trait and what is a conduct. Arguably, impulsivity and aggressiveness are dispositions, aggression is an observable behavior, and an impulse is a drive. (c) It could be argued that the finding that impulsive and aggressive behaviors are linked to common underlying biological mechanisms (Frankle et al., 2005 and Seroczynski et al., 1999) could have led investigators to think that both constructs are highly related, even to consider that they function as a single trait-like dimension. In order to solve this puzzle, Critchfield et al. (2004) examined relationships between impulsivity, aggression and impulsive aggression in borderline personality disorder. Using principal components analysis, they explored impulsive aggression as a single phenotypic dimension, finding that impulsivity and aggressiveness/aggression were separate constructs. However, they used a small clinical sample which led them to state that their results should be regarded with caution.