Aggression
Aggression is a behavior aimed at opposing or attacking something or someone. Though often done with the intent to cause harm, it can be channeled into creative and practical outlets for some.[1] It may occur either reactively or without provocation. In humans, aggression can be caused by various triggers. For example, built-up frustration due to blocked goals or perceived disrespect.[2] Human aggression can be classified into direct and indirect aggression; whilst the former is characterized by physical or verbal behavior intended to cause harm to someone, the latter is characterized by behavior intended to harm the social relations of an individual or group.[3][4][5]
"Aggressive" and "Aggressive behavior" redirect here. For other uses, see Aggressive (disambiguation), Aggression (disambiguation), and Aggressive Behavior (journal).
In definitions commonly used in the social sciences and behavioral sciences, aggression is an action or response by an individual that delivers something unpleasant to another person.[6] Some definitions include that the individual must intend to harm another person.[7]
In an interdisciplinary perspective, aggression is regarded as "an ensemble of mechanism formed during the course of evolution in order to assert oneself, relatives or friends against others, to gain or to defend resources (ultimate causes) by harmful damaging means. These mechanisms are often motivated by emotions like fear, frustration, anger, feelings of stress, dominance or pleasure (proximate causes). Sometimes aggressive behavior serves as a stress relief or a subjective feeling of power."[8][9] Predatory or defensive behavior between members of different species may not be considered aggression in the same sense.
Aggression can take a variety of forms, which may be expressed physically, or communicated verbally or non-verbally: including anti-predator aggression, defensive aggression (fear-induced), predatory aggression, dominance aggression, inter-male aggression, resident-intruder aggression, maternal aggression, species-specific aggression, sex-related aggression, territorial aggression, isolation-induced aggression, irritable aggression, and brain-stimulation-induced aggression (hypothalamus). There are two subtypes of human aggression: (1) controlled-instrumental subtype (purposeful or goal-oriented); and (2) reactive-impulsive subtype (often elicits uncontrollable actions that are inappropriate or undesirable). Aggression differs from what is commonly called assertiveness, although the terms are often used interchangeably among laypeople (as in phrases such as "an aggressive salesperson").[10]
Overview[edit]
Dollard et al. (1939) proposed that aggression was due to frustration, which was described as an unpleasant emotion resulting from any interference with achieving a rewarding goal.[11] Berkowitz[12] extended this frustration–aggression hypothesis and proposed that it is not so much the frustration as the unpleasant emotion that evokes aggressive tendencies, and that all aversive events produce negative affect and thereby aggressive tendencies, as well as fear tendencies. Besides conditioned stimuli, Archer categorized aggression-evoking (as well as fear-evoking) stimuli into three groups; namely, pain, novelty, and frustration, although he also described "looming", which refers to an object rapidly moving towards the visual sensors of a subject, and can be categorized as "intensity."[13]
Aggression can have adaptive benefits or negative effects. Aggressive behavior is an individual or collective social interaction that is a hostile behavior with the intention of inflicting damage or harm.[3][4] Two broad categories of aggression are commonly distinguished. One includes affective (emotional) and hostile, reactive, or retaliatory aggression that is a response to provocation, and the other includes instrumental, goal-oriented or predatory, in which aggression is used as a means to achieve a goal.[14] An example of hostile aggression would be a person who punches someone who insulted him or her. An instrumental form of aggression would be armed robbery. Research on violence from a range of disciplines lend some support to a distinction between affective and predatory aggression.[15] However, some researchers question the usefulness of a hostile versus instrumental distinction in humans, despite its ubiquity in research, because most real-life cases involve mixed motives and interacting causes.[16]
A number of classifications and dimensions of aggression have been suggested. These depend on such things as whether the aggression is verbal or physical; whether or not it involves relational aggression such as covert bullying and social manipulation;[17] whether harm to others is intended or not; whether it is carried out actively or expressed passively; and whether the aggression is aimed directly or indirectly. Classification may also encompass aggression-related emotions (e.g., anger) and mental states (e.g., impulsivity, hostility).[18] Aggression may occur in response to non-social as well as social factors, and can have a close relationship with stress coping style.[19] Aggression may be displayed in order to intimidate.
The operative definition of aggression may be affected by moral or political views. Examples are the axiomatic moral view called the non-aggression principle and the political rules governing the behavior of one country toward another.[20] Likewise in competitive sports, or in the workplace, some forms of aggression may be sanctioned and others not (see Workplace aggression).[21] Aggressive behaviors are associated with adjustment problems and several psychopathological symptoms such as antisocial personality disorder, borderline personality disorder, and intermittent explosive disorder.[22]
Biological approaches conceptualize aggression as an internal energy released by external stimuli, a product of evolution through natural selection, part of genetics, a product of hormonal fluctuations. Psychological approaches conceptualize aggression as a destructive instinct, a response to frustration, an affect excited by a negative stimulus, a result of observed learning of society and diversified reinforcement, a resultant of variables that affect personal and situational environments.[23][24]
Etymology[edit]
The term aggression comes from the Latin word aggressio, meaning attack. The Latin was itself a joining of ad- and gradi-, which meant step at. The first known use dates back to 1611, in the sense of an unprovoked attack.[25]
A psychological sense of "hostile or destructive behavior" dates back to a 1912 English translation of Sigmund Freud's writing.[26] Alfred Adler theorized about an "aggressive drive" in 1908. Child raising experts began to refer to aggression, rather than anger, from the 1930s.[27]
Physiology[edit]
Brain pathways[edit]
Many researchers focus on the brain to explain aggression. Numerous circuits within both neocortical and subcortical structures play a central role in controlling aggressive behavior, depending on the species, and the exact role of pathways may vary depending on the type of trigger or intention.[75][4]
In mammals, the hypothalamus and periaqueductal gray of the midbrain are critical areas, as shown in studies on cats, rats, and monkeys. These brain areas control the expression of both behavioral and autonomic components of aggression in these species, including vocalization. Electrical stimulation of the hypothalamus causes aggressive behavior[76] and the hypothalamus has receptors that help determine aggression levels based on their interactions with serotonin and vasopressin.[77] In rodents, activation of estrogen receptor-expressing neurons in the ventrolateral portion of the ventromedial hypothalamus (VMHvl) was found to be sufficient to initiate aggression in both males and females.[78][79] Midbrain areas involved in aggression have direct connections with both the brainstem nuclei controlling these functions, and with structures such as the amygdala and prefrontal cortex.
Stimulation of the amygdala results in augmented aggressive behavior in hamsters,[80][81] while lesions of an evolutionarily homologous area in the lizard greatly reduce competitive drive and aggression (Bauman et al. 2006).[82] In rhesus monkeys, neonatal lesions in the amygdala or hippocampus results in reduced expression of social dominance, related to the regulation of aggression and fear.[83] Several experiments in attack-primed Syrian golden hamsters, for example, support the claim of circuitry within the amygdala being involved in control of aggression.[81] The role of the amygdala is less clear in primates and appears to depend more on situational context, with lesions leading to increases in either social affiliatory or aggressive responses. Amygdalotomy, which involves removing or destroying parts of the amygdala, has been performed on people to reduce their violent behaviour.
The broad area of the cortex known as the prefrontal cortex (PFC) is crucial for self-control and inhibition of impulses, including inhibition of aggression and emotions. Reduced activity of the prefrontal cortex, in particular its medial and orbitofrontal portions, has been associated with violent/antisocial aggression.[84] In addition, reduced response inhibition has been found in violent offenders, compared to non-violent offenders.[75]
The role of the chemicals in the brain, particularly neurotransmitters, in aggression has also been examined. This varies depending on the pathway, the context and other factors such as gender. A deficit in serotonin has been theorized to have a primary role in causing impulsivity and aggression. At least one epigenetic study supports this supposition.[85] Nevertheless, low levels of serotonin transmission may explain a vulnerability to impulsiveness, potential aggression, and may have an effect through interactions with other neurochemical systems. These include dopamine systems which are generally associated with attention and motivation toward rewards, and operate at various levels. Norepinephrine, also known as noradrenaline, may influence aggression responses both directly and indirectly through the hormonal system, the sympathetic nervous system or the central nervous system (including the brain). It appears to have different effects depending on the type of triggering stimulus, for example social isolation/rank versus shock/chemical agitation which appears not to have a linear relationship with aggression. Similarly, GABA, although associated with inhibitory functions at many CNS synapses, sometimes shows a positive correlation with aggression, including when potentiated by alcohol.[86][87]
The hormonal neuropeptides vasopressin and oxytocin play a key role in complex social behaviours in many mammals such as regulating attachment, social recognition, and aggression. Vasopressin has been implicated in male-typical social behaviors which includes aggression. Oxytocin may have a particular role in regulating female bonds with offspring and mates, including the use of protective aggression. Initial studies in humans suggest some similar effects.[88][89]
In human, aggressive behavior has been associated with abnormalities in three principal regulatory systems in the body serotonin systems, catecholamine systems, and the hypothalamic–pituitary–adrenal axis. Abnormalities in these systems also are known to be induced by stress, either severe, acute stress or chronic low-grade stress[90]