Abstract:

Reactive aggression has been widely concerned by researchers because of its serious impact on society, such as violent crimes. Existing neuroimaging studies using patients with high levels of aggression indicated a network of brain regions subserve reactive aggression, including amygdala, caudate nucleus, and orbitofrontal cortex. Furthermore, researchers believed that reduced prefrontal activity along with heightened subcortical activity in the context of provocative stimuli poses an increased risk for reactive aggression. However, evidence for this theory in healthy population is lacking, especially this independently of the experiment task.

In this study, the modified TAP was used and the punishment levels selected for the virtual opponents serve as indicator of reactive aggression. Based on the previous researches, Orbitomedial Prefrontal (OMPFC) was selected as the seed to investigate the relationship of reactive aggression and the connectivity between OMPFC and other brain regions using resting state fMRI. Thirty-night undergraduates (mean age = 20.05 ± 0.92 years old) were enrolled in the experiment. The resting state functional magnetic resonance (rs-fMRI) data was acquired using Echo Planar Imaging (EPI) sequence from a 3-T Siemens Magnetom Trio scanner (Siemens Medical, Erlangen, Germany). This scanning acquired 242 volumes with TR = 2 s (lasting 8 min and 8 sec). rs-fMRI data was processed and analyzed using the REST (Resting-State fMRI Data Analysis Toolkit) toolbox to calculate Functional Connectivity (FC) and Granger Causality Analysis (GCA), which reflects the functional and effective connectivity among different areas, respectively. The results of FC indicated that the functional connectivity between the left OMPFC and right angular gyrus, left OMPFC and bilateral caudate nucleus, right OMPFC and right caudate nucleus were significantly correlated with the reactive aggression. Furthermore, the follow-up GCA indicated that the effective connectivity of right caudate nucleus to the right OMPFC was correlated significantly with reactive aggression, especially in the provocative condition.

The caudate nucleus plays an important role in flexibly responding to the environment. It is activated in response to reward. When the individuals thought the aggression was valuable and seemed to receive reward after the aggression, the caudate nucleus was also activated. Furthermore, a study combined PET and fMRI and revealed a strong relationship between the caudate nucleus and cortical areas associated with executive functioning (i.e., the function of prefrontal cortex). Another study demonstrated that violent offenders behaved more aggressively and showed significantly higher brain reactivity to provocations within the caudate nucleus, as well as reduced caudate nucleus-prefrontal cortex connectivity. To sum up, these results suggest that the connectivity between OMPFC and caudate nucleus is closely related to reactive aggression. It provides some evidence for further revealing the neural mechanism of reactive aggression, and firstly made a systematic analysis of reactive aggression using resting state functional connectivity and effective connectivity.

Key words: reactive aggression, resting-state fMRI, functional connectivity, effective connectivity, Granger causality analysis, OMPFC, caudate nucleus