The ability to successfully suppress impulses and angry affect is fundamental to control aggressive reactions following provocations. The aim of this study was to examine neural responses to provocations and aggression using a laboratory model of reactive aggression. We used a novel functional magnetic resonance imaging point-subtraction aggression paradigm in 44 men, of whom 18 were incarcerated violent offenders and 26 were control non-offenders. We measured brain activation following provocations (monetary subtractions), while the subjects had the possibility to behave aggressively or pursue monetary rewards. The violent offenders behaved more aggressively than controls (aggression frequency 150 vs 84, P = 0.03) and showed significantly higher brain reactivity to provocations within the amygdala and striatum, as well as reduced amygdala-prefrontal and striato-prefrontal connectivity. Amygdala reactivity to provocations was positively correlated with task-related behavior in the violent offenders. Across groups, striatal and prefrontal reactivity to provocations was positively associated with trait anger and trait aggression. These results suggest that violent individuals display abnormally high neural sensitivity to social provocations, a sensitivity related to aggressive behavior. These findings provide novel insight into the neural pathways that are sensitive to provocations, which is critical to more effectively shaped interventions that aim to reduce pathological aggressive behavior.

The Point Subtraction Aggression Paradigm (PSAP) measures aggressive behavior in response to provocations. The aim of the study was to implement the PSAP in a functional neuroimaging environment (fMRI) and evaluate aggression-related brain reactivity including response to provocations and associations with aggression within the paradigm. Twenty healthy participants completed two 12-min PSAP sessions within the scanner. We evaluated brain responses to aggressive behavior (removing points from an opponent), provocations (point subtractions by the opponent), and winning points. Our results showed significant ventral and dorsal striatal reactivity when participants won a point and removed one from the opponent. Provocations significantly activated the amygdala, dorsal striatum, insula, and prefrontal areas. Task-related aggressive behavior was positively correlated with neural reactivity to provocations in the insula, the dorsal striatum, and prefrontal areas. Our findings suggest the PSAP within an fMRI environment may be a useful tool for probing aggression-related neural pathways. Activity in the amygdala, dorsal striatum, insula, and prefrontal areas during provocations is consistent with the involvement of these brain regions in emotional and impulsive behavior. Striatal reactivity may suggest an involvement of reward during winning and stealing points.

Developing positron emission tomography (PET) radioligands for the detection of endogenous serotonin release will enable the investigation of serotonergic deficits in many neuropsychiatric disorders. The present study investigates how acute challenges that aim to increase or decrease cerebral serotonin levels affect binding of the serotonin 2A receptor (5-HT 2A R) agonist radioligand [ 11 C]Cimbi-36. In a randomized, double-blind, placebo-controlled, three-arm design, 23 healthy volunteers were PET scanned twice with [ 11 C]Cimbi-36: at baseline and following double-blind assignment to one of three interventions (1) infusion of the selective serotonin reuptake inhibitor (SSRI) citalopram preceded by oral dosing of the 5-HT 1A R antagonist pindolol, ( n = 8) (2) acute tryptophan depletion (ATD) ( n = 7) and (3) placebo ( n = 8). Two-sample t-tests revealed no significant group differences in percent change of neocortical [ 11 C]Cimbi-36 binding from baseline to intervention between placebo and citalopram/pindolol ( p = 0.4) or between placebo and ATD ( p = 0.5). Notably, there was a significantly larger within-group variation in 5-HT 2A R binding after intervention with citalopram/pindolol, as compared with placebo ( p = 0.007). These findings suggest that neither ATD nor a combination of citalopram and pindolol elicit acute unidirectional changes in serotonin levels sufficient to be detected with [ 11 C]Cimbi-36 PET in neocortex. We suggest that the large interindividual variation in 5-HT 2A R binding after citalopram/pindolol reflects that after an acute SSRI intervention, individuals respond substantially different in terms of their brain serotonin levels. Our observation has a potential impact for the understanding of patient responses to SSRI.