1.3.1 Appetitive aggression in war and violent conflict
For combatants and soldiers, war and armed conflict are not just confined to experiencing and witnessing violence. Involvement in these events also includes perpetrating violence such as harming and killing others. Like other conflicts in East-Africa, the Burundian war was characterized by extreme cruelty and brutality (Uvin, 2009). Fighting was not restricted to the battlefield and atrocities and massacres against the civilian population were common. Horrific methods of killing and torture were reported. The perpetrated atrocities often went far beyond a defensive behavior that would be taken to save one's own life when being attacked or serve to gain victory during a battle or control over a region or population. Reports of former combatants and individuals actively involved in violence revealed underlying emotions like excitement and pleasure associated with violent perpetration rather than fear and horror (Elbert et al., 2010; Silva, Derecho, Leong, Weinstock, & Ferrari, 2001). Similar testimonies exist across various wars and conflict regions. Indeed, the perpetration of acts of extreme violence was typically not restricted to single cases, but was found to be rather prevalent in armed groups and even in the general population (Schaal, Heim, & Elbert, 2014; Weierstall, Castellanos, Neuner, & Elbert, 2013).
How can violence arise to such an extreme level? Elbert and colleagues (2010) stated, that the aggressive act itself, with all included cues such as the victim's suffering and screaming, and bloody wounds, may be intrinsically rewarding and thus reinforcing the urge and desire to kill, torture, and mutilate. This lust-driven type of aggressive behavior is termed appetitive aggression (Elbert et al., 2010). Appetitive aggression is considered to be a proactive type of aggression, characterized by an approach and attraction to violence and underlying emotions like pleasure, lust and fascination (Elbert et al., 2010; Weierstall & Elbert, 2011). In contrast, the aforementioned aggressive behavior occurring as a reaction to life-threat and PTSD is triggered by a perceived threat in the sense of a defense reaction. This affective and impulsive form of aggression is often referred to as reactive aggression (Anderson & Bushman, 2002;
Fontaine, 2007; Poulin & Boivin, 2000). Violent outbursts and escalations seem hence to be determined by both fear and pleasure driven mechanisms of aggression. The extreme brutality and cruelty may however mainly be rooted in the appetitive type of aggression. This assumption is supported by several studies which found appetitive aggression to be widespread in combatants of various conflict areas (e.g., Weierstall et al., 2013; Weierstall, Schalinski, Crombach, Hecker, & Elbert, 2012) and strongly related to violent perpetration.
For example, Hecker and colleagues demonstrated that appetitive aggression was correlated with self-committed violence in former combatants of the DR Congo (Hecker, Hermenau, Maedl, Elbert, & Schauer, 2012). Further studies with combatants of the DR Congo and
(Chemtob et al., 1997; Chemtob et al., 1988), an "aggressor mode" is assumed when referring to appetitive aggression (Elbert et al., 2010). After an armed conflict has ended or combatants have left the armed group, a switching back to the "aggressor mode" can occur, even if such a switch were unintended. Even though violent perpetration and the positive emotions related to it shall be inhibited in civil life, common salient cues can trigger these emotions and, as a result, lead to aggressive outbursts. At the same time, the experience of positive emotions while perpetrating violence within an armed group may mean that some combatants actively seek situations where committing violence is possible. Combatants' reports indicate that violence and killing can indeed be "addictive" (Elbert et al., 2010). A hunting network, similar to the aforementioned fear network, may explain the switch back to the "aggressor mode". Here, violent cues are integrated into a network of sensations, cognitions, and physiological components. However, re-exposure to similar violent cues does not evoke an alarm response but rather elicits an appetitive arousal.
1.3.2 Appetitive aggression and PTSD
In the past, it was debated whether the perpetration of violence is as traumatic as experiencing violence as a victim or even has a higher traumatizing potential. Several studies could demonstrate that self-perpetrated violence and killing in war induce symptoms of PTSD, even after controlling for combat exposure (Dohrenwend, Yager, Wall, & Adams, 2013; Maguen et al., 2010; Van Winkle & Safer, 2011). However, in populations where appetitive aggression was prevalent, this relationship could not be found (Köbach et al., 2014;
Weierstall et al., 2011) or could only be found for forcibly recruited combatants, but not for combatants who volunteered themselves (Hecker, Hermenau, Maedl, Hinkel, Schauer, &
Elbert, 2013). These results indicate that appetitive aggression may be a decisive factor for the potential of killing and atrocities to be traumatic. Appetitive aggression is assumed to serve as a protective mechanism that counters the integration of violent cues into the fear
network and embeds them in the hunting network instead. Therefore, the development of PTSD symptoms may be prevented. Previous research found a negative relationship between the level of appetitive aggression and PTSD symptom severity in Rwandan genocide perpetrators (Weierstall et al., 2011), German soldiers of WWII (Weierstall, Huth, Knecht, Nandi, Elbert, 2012) and different populations of combatants and child soldiers in DR Congo, Uganda, and Columbia (Hecker et al., 2013; Weierstall et al., 2013; Weierstall et al., 2012).
However, symptoms of PTSD still develop when the trauma load exceeds a certain threshold.
Violent events as either perpetrator or victim share many common cues. When exposed to ongoing violence, elements of the fear and hunting network begin to overlap so that violent cues begin to trigger a fear reaction.