October 04, 2004
Stress And Violence Feed Back In Vicious Cycle

Hormonal and neural chances caused by stress and aggression feed back on each other and promote each other.

WASHINGTON -- 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."

They add that the resulting vicious cycle "would explain why aggressive behavior escalates so easily and is so difficult to stop once it has started, especially because corticosteroids rapidly pass through the blood-brain barrier." The findings suggest that even when stress hormones spike for reasons not related to fighting, they may lower attack thresholds enough to precipitate violent behavior. That argument, if extended in research to humans, could ultimately explain on the biological level why a bad day at the office could prime someone for nighttime violence toward family members.

Stress reaction is one of the evolutionary legacies of human evolution that in modern conditions is mostly maladaptive. Most people who get angry or frustrated and therefore feel stress are not benefitting and are even being harmed by the stress. We need better biotechnological tools for suppressing stress response. This would do more than reduce the incidence of acts of violence. Heart disease, general aging, depression, and other maladies would occur less frequently if stress responses happened less often.

Regarding my previous post on car cruise controls and automated driving: One of the benefits of being able to turn driving over to computers would be a reduction in feelings of stress. The stress of fighting commuter traffic comes on top of stresses associated with work and home life. Lower levels of stress made possible by automated driving computers would reduce both illness and violence.

Share |      Randall Parker, 2004 October 04 12:25 PM  Brain Violence

Alexander Williams said at October 4, 2004 12:45 PM:

Its also worth suggesting that manipulating the stress response could have long-term negative productivity and/or creativity impacts. Some people (like myself), respond very well and actively to stress, even if it elevates our violence response. In fact, considering the employment in which stress is legitimately incurred, most active violence/high activity responses are not only valid, they're vital.

What the core problem seems to be is inappropriate stressors. Couple that with a society that focuses on eliminating stress instead of building proper responses into the individual, and you have a recipe for maladaption.

Patri Friedman said at October 4, 2004 6:42 PM:

I've thought about taking beta-blockers to reduce the stress response, at least the adrenaline-modulated portion of it. Unfortunately that has negative effects on asthma. Rumour has it that professional billiards players have become quite fond of beta-blockers lately. I've wondered if they'd be good for poker players, who compete in an arena where stress responses have a directly negative effect on performance.

I definitely agree with you that stress is mainly maladaptive.

Peter said at October 5, 2004 5:51 AM:

I wonder if the people who thrive on stress, are really addicted to the endorphins/other neurotransmitters that flush around when stressed. My experience from very high fight/flight stress situations leaves me shaking and with splitting headaches, similar to the shakes and headaches I get when I have caffeine withdrawals.

Joshua Allen said at October 12, 2004 10:57 AM:

Jeez, the experiment just showed that the two *biological* factors act in a feedback loop. That is hardly sufficient to jump to conclusions about computers driving cars or high stress jobs.

In humans, stress is almost entirely cognitive (i.e. "gestalt"). You have a choice about whether or not to be stressed by driving, and that choice remarkably extends to the vast majority of human activities. Just imagine yourself to be Laura's papa in "Little House on the Prairie", trekking to the trading post on foot through blizzards and attacks by scalp-hungry savages. Now transport yourself to the present, as you smoothly ride along in your own private technological wonder, listening to classical music or a book on tape. Don't you feel relieved to be riding in a car?

Of course, I agree that biological imbalances can cause poorly-tuned Gestalts, which lead to unhelpful interpretations of events (ala the "Point Subtraction Aggression Paradigm" tests). So whan I say that you "choose" to view driving as a relaxing pleasure, that is only to the extent that your biology does not interfere. However, there is ample evidence that the cognitive has significant influence over the biological, and this is where we should always start, rather than jumping immediately to the blunt instrument of biological manipulation. I have done much informal research about tweaking various neurotransmitter and adrenocortical hormone balances. Although people think of the antidepressants and particularly SSRIs, this is just one tiny piece of the puzzle, and "depression" is just an ill-defined bucket that only captures a fraction of the prism of cognitive gestalt. You cannot talk about these things without also looking at noradrenaline, norepinephrine, choline levels, and then realizing that certain drugs which act on the exact same systems ostensibly can have such drastically different facets of effect. Even across people -- give one person Reboxetine and he turns into a productive an motivated individual, and give another the same drug and he turns into a panic-attack disaster. The balance between stress and motivation is extremely delicate, in my experience, and it is very difficult to shut down one without screwing up the the other through biological/neurochemical means. I also think that most theories which project neurochemical explanations onto cognitive/gestalt functions are laughable fictions.

Randall Parker said at October 12, 2004 11:09 AM:


Yet some people get stressed by driving their cars. Therefore reducing their need to drive would reduce the level of stress that they feel.

Yes, as you point out, the conscious minds in many people very often fail to choose interpretations of events that avoid feelings of stress, depression, anxiety or other negative emotions.

A reaction to a given situation can be deterministic for some people without being deterministic for other people.

Post a comment
Name (not anon or anonymous):
Email Address:
Remember info?

Go Read More Posts On FuturePundit
Site Traffic Info
The contents of this site are copyright