What's the science?
Injury or impairment of the prefrontal cortex is known to be a risk factor for aggressive and antisocial behaviour, including aggressive sexual behaviour. In particular, the dorsolateral prefrontal cortex (DLPFC) is known to play a role in aggressive behaviour, however, the neuroimaging evidence for this is correlational rather than causal. The causal role of the DLPFC on aggressive behaviour is not known. This week in the Journal of Neuroscience, Choy and colleagues used transcranial direct current stimulation (tDCS) to stimulate the DLPFC and assess intent to commit aggressive behaviour.
How did they do it?
The authors designed a double-blind randomized trial in which anodal, active tDCS and sham tDCS (as a placebo) were administered bilaterally to the DLPFC. Eighty-one healthy adults were included in the final sample. A standard 20-minute tDCS protocol was applied to half of the participants, while the other half received sham tDCS, in which the stimulation was turned off after the first 30 seconds. Participants then completed questionnaires in which they a) read scenarios describing physical or sexual aggression and described how likely they would be to commit them and b) rated how morally wrong it would be to act in an aggressive scenario. Participants were also given a ‘voodoo doll’ and asked how much ‘negative energy’ they would like to release by inserting pins into the doll, which represents a family member or close friend. Finally, they assess whether moral wrongfulness mediated the group differences (active tDCS versus sham tDCS) in intent to commit an aggressive act. Participants also self-reported previous criminal activity and baseline aggression levels.
What did they find?
Participants in the active tDCS group were less likely to report intent to engage in aggressive acts, physical assault, and sexual assault compared to participants in the sham tDCS group after controlling for baseline criminal activity and aggression levels. No differences between groups on the voodoo doll aggression task were found. The active tDCS group perceived aggressive acts as more morally wrong, and moral wrongfulness partly mediated the relationship between group and intent to commit aggressive acts. Moral wrongfulness also mediated the relationship between group and intent to commit sexual but not physical assault.
What's the impact?
This is the first study to assess the effects of tDCS of the DLPFC on aggressive intent. Further, the perception of these acts as immoral mediated the relationship between tDCS stimulation and aggression. Damage to the prefrontal cortex is a known risk factor for aggressive behaviour, so understanding the causal role of the DLPFC in inhibiting aggression is critical for addressing aggression as a public health issue and for disorders such as antisocial and borderline personality disorders.
Choy et al., Stimulation of the Prefrontal Cortex Reduces Intentions to Commit Aggression: A Randomized, Double-Blind, Placebo-Controlled, Stratified, Parallel-Group Trial. Journal of Neuroscience (2018). Access the original scientific publication here.