Scientists may be learning why it’s so hard to stop the cycle of violence. The answer may lie in the nervous system.
There appears to be a fast, mutual, positive feedback loop between stress hormones and a brain-based aggression-control center in rats, whose neurophysiology is similar to ours. It may explain why, under stress, humans are so quick to lash out and find it hard to cool down. The findings, which could point to better ways to prevent pathological violence, appear in the October issue of Behavioral Neuroscience, which is published by the American Psychological Association (APA).
In five experiments using 53 male rats, behavioral neuroscientists from the Netherlands and Hungary studied whether stimulating the brain’s aggression mechanism raised blood levels of a stress hormone and whether higher levels of the same hormone led to the kind of aggression elicited by that mechanism. The results showed a fast-acting feedback loop; the mechanism works in both directions and raising one variable raises the other. Thus, stress and aggression may be mutually reinforcing, which could explain not only why something like the stress of traffic jams leads to road rage, but also why raging triggers an ongoing stress reaction that makes it hard to stop.
In the study, the scientists electrically stimulated an aggression-related part of the rat hypothalamus, a mid-brain area associated with emotion. The rats suddenly released the stress hormone corticosterone (very like cortisol, which humans release under stress) -- even without another rat present. Normally, rats don’t respond like that unless they face an opponent or another severe stressor.
Says lead author Menno Kruk, PhD, “It is well known that these stress hormones, in part by mobilizing energy reserves, prepare the physiology of the body to fight or flee during stress. Now it appears that the very same hormones ‘talk back’ to the brain in order to facilitate fighting.”
To study the hypothesized feedback loop from the other direction, the scientists removed the rats’ adrenal glands to prevent any natural release of corticosterone. Then researchers injected the rats with corticosterone. Within minutes of injection, the hormone facilitated stimulation-evoked attack behavior.
Thus, in rapid order, stimulating the hypothalamic attack area led to higher stress hormones and higher stress hormones led to aggression – evidence of the feedback loop within a single conflict. Write the authors, “Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions.”