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Background The direct execution as well as the visual perception of violence can have a hedonistic aspect and elicit positive arousal. ( Elbert et al., 2010 ) So far, neurobiological correlates of this “appetitive” form of aggression have not been investigated in healthy subjects. Using functional magnetic resonance imaging (fMRI), we tested if subjects who act violently (martial artists) showed greater brain responses to violent images compared to controls in the subcortical reward-associated areas of the mesolimbic dopaminergic system. ( Urban et al., 2012 ). Methods Sixteen male martial artists and 26 male controls took part in the study. As a measure of aggressiveness, we used the FAF questionnaire (“Fragebogen zur Erfassung von Aggressivitätsfaktoren”). During our event-related fMRI paradigm, 54 violent and 54 neutral pictures were shown in a randomized order. After their presentation, a square or circle was briefly projected on the pictures and the subjects then decided which shape had been shown by pressing a button. Independent of their response, a reward randomly followed their answer in 50% of trials. A first-level general linear model (GLM) analysis was run, obtaining the contrast values for violent > neutral pictures. Average contrast values were then extracted from the bilateral nucleus accumbens, amygdala and orbitofrontal cortex (OFC). These values were entered in a GLM to investigate main effects and interactions of the group factor and FAF scores, using age as a covariate. Results Across all participants, higher aggressiveness scores were associated with less activation of the bilateral OFC while watching violent pictures in contrast to neutral ones (left OFC: F df=1 = 4.201, p = .048; right OFC: F df=1 = 4.097, p = .050). On average, martial artists had a higher activation in the left amygdala while watching violent pictures in contrast to controls ( F df=1 = 13.333, p = .001). Furthermore, the more aggressive martial artists were, the smaller their activation in the left amygdala in this condition ( F df=1 = 7.998, p = .008). Discussion Activations in the OFC have been linked to emotional regulation. ( Philipps et al., 2008 ) While watching violent pictures, more aggressive people might show a reduced frontal inhibition of subcortical areas involved in emotion generation. The amygdala is activated by presentation of affective and motivationally triggering stimuli ( Rosell and Siever, 2015 ), e.g. watching a fight between two people. There might be different mechanisms in both groups to deal with aggression. [ABSTRACT FROM AUTHOR]

Theoretical background Perception and practice of violence have, aside from reactive components, also hedonistic aspects that are associated with positive arousal (appetitive aggression). Earlier studies have predominantly investigated the etiology of aggressive behavior in forensic and psychiatric patients. The present study examined structural brain abnormalities in healthy people inclined to violence (martial artists) compared to healthy controls not showing violent behavior. Methods Aggressiveness was assessed in 21 male healthy martial artists and 26 age-matched male healthy controls using the Freiburg personality inventory (FPI-R) and the aggressivity factors questionnaire (FAF). Participants then underwent structural T1-weighted MRI scanning. Differences in local gray matter (GM) were analyzed using voxel-based morphometry (VBM). A whole-brain analysis of the main effects of group and aggressivity (FAF) as well as their interaction was computed, using a threshold of p < .001, followed by a cluster-level p FWE < .05 to account for multiple comparisons. All analyses were controlled for age and total intracranial volume. Results There was no significant main effect of group or aggressiveness in predicting GM concentration. Nevertheless, an interaction effect between group and aggressiveness was evident in a cluster comprising the left temporal pole and left inferior temporal gyrus ( F -test, whole-brain: p < .001, cluster-level: p FWE = .017; Fig. 1 ). Post-hoc analysis revealed a significant negative partial correlation between aggressiveness and mean GM concentration within the cluster in martial artists ( r = −.71, p = .001) and a significant positive one in healthy controls ( r = .54, p = .007) ( Fig. 2 ). Discussion Martial artists and controls displayed opposite correlations between aggressiveness and temporal GM: while they were positively correlated in controls, they correlated inversely in martial artists. Earlier studies reported decreased regional GM volumes in this region within diverse aggressive psychiatric populations, for example patients affected by psychopathy (Ermer et al., 2013) or impulsive-aggressive personality disorder ( Dolan et al., 2002 ). The temporal pole and inferior temporal gyrus are relevant for emotional regulation and aggression control ( Dolan et al., 2002 ) and display alterations in antisocial or violent behavior ( Wong et al., 1997 ). The increased GM concentration of these areas in aggressive healthy controls might reflect a stronger top-down inhibition of their aggressivity. Martial artists, on the other hand, might be able to release their aggressivity in fights, thus showing reduced need for regulation and lower GM concentration in this region. [ABSTRACT FROM AUTHOR]