WASHINGTON, Feb. 15 (UPI) -- Some perpetrators of domestic violence may suffer from a nervous system irregularity that makes it harder for them to control emotions and aggression, according to a study published in the journal Psychophysiology. It appeared in the March issue.
"Although many link domestic violence to alcohol or to learned behavior patterns such as witnessing violence, the majority of abusers are sober when they are violent," the study's lead author, Dr. John C. Umhau, of the National Institute on Alcohol Abuse and Alcoholism, in Bethesda, Md., told United Press International on Friday. "Many who exhibit violent behavior say that a look or a statement perceived as a threat can trigger an outburst.
"This perceived threat exhibits the same reaction to fear with trembling, voice changes, breathlessness, palpitations and flushing which is not under their conscious control."
Umhau and colleagues focused their analysis on two measures of the autonomic nervous system: heart rate and vagal nerve activity, which is one of several heart-rate regulators.
These symptoms, characteristic of ANS arousal, are out of proportion to environmental stimuli and are not under the perpetrator's conscious control, according to Umhau.
"The vagus responds rapidly to changing metabolic demands, whether from agitated emotional arousal or from a simple posture change, and immediately adjusts heart rate," said Umhau.
There is also a trend toward a greater diastolic blood pressure response in perpetrators that suggests there may be altered central regulation of the baroreceptor reflex.
This reflex is modulated by the hypothalamus in the brain. Electrical stimulation of the medial hypothalamus in a cat inhibits this reflex with the onset of rage, i.e., raised fur, broad-sided stance, arched back, loud vocalizations, unsheathing of the claws.
"We believe this constellation of symptoms in the cat is analogous to the intimidating behaviors displayed by perpetrators at the time of domestic violence," Umhau said. "If this is the case, it is conceivable that pathways mediating their aggressive behavior are chronically dysregulated, and interfere with normal baroreceptor function even when perpetrators do not outwardly appear enraged."
Sixteen domestic violence perpetrators were recruited for the study through a newspaper advertisement along with two comparison groups -- 13 nonviolent alcoholics and 15 healthy volunteers. The perpetrators underwent tests to rule out central nervous system damage or brain disorders such as schizophrenia.
All study participants were asked to complete a simple task: to go from bed rest to standing quietly by their bedside for five minutes. The act of standing up is a natural physiological stressor that raises heart rate. Umhau monitored the study participants' heart rate and vagal nerve activity on a minute-by-minute basis as they stood beside their beds.
There were no significant group differences for age, weight, height or socioeconomic status. The healthy volunteers smoked less and consumed significantly less alcohol than the perpetrators and the alcoholics, who did not differ from each other on these variables.
Each group exhibited a significant increase in heart rate upon standing. Standing elicited a significant decrease in vagal influences to the heart.
As with the healthy volunteers, the nonviolent alcoholic group showed a correlation between decreases in vagal nerve activity and increases in heart rate, but this correlation did not reach statistical significance.
"But the perpetrators of domestic violence showed a different neural strategy in the regulation of heart rate during a posture shift," said Umhau. "Future studies may confirm that altered heart rate regulation provides a measurable index of autonomic dysregulation, which in turn, may be found to affect the perpetrators' ability to modulate emotion and to control aggression."
Umhau speculated that the faulty regulation observed in the heart rates of the violent study participants may also exist in other body parts involved in the expression of emotion and rage, such as the larynx, pharynx, esophagus and bronchi.
"Future studies may confirm that altered heart rate regulation provides a measurable index of autonomic dysregulation, which, in turn, may be found to affect the perpetrators' ability to modulate emotion and to control aggression," Umhau said. "This is just one piece of the puzzle because we don't know what triggers violence and why some people can stop on their own and some can't."
Domestic violence occurs worldwide and has vast social and medical consequences wrecking relationships and getting people in trouble with the law.
"It's my understanding that most data supports what was found in the study as does my personal experience," Dr. Rahn Bailey, a forensic psychiatrist with the University of Texas Medical School at Houston, told UPI. "We don't know what the stressor will be to trigger violence domestic or otherwise, but I am shocked at what little provocation it takes to ignite violence in any situation, lately."
"In the United States, an estimated 30 percent of all women who are murdered are killed by their husbands, boyfriends or former partners and acts of domestic violence account for at least 20 percent of all emergency room visits," according to Umhau.
"Many people are afraid of someone homeless who may have a mental problem but a person is far more likely to be attacked by a relative because of the proximity and because a relative will least likely turn a person into the police," Bailey said.
Domestic violence is currently treated by antidepressive drugs and therapy.
(Reported by Alex Cukan in Albany, N.Y.)
