By BENEDICT CAREY
Play hooky, disappear for the weekend, have a fling, binge-shop like a Wall Street divorcée. Spontaneity can be a healthy defiance of routine, an expression of starved desire, some psychologists say.
Yet for scientists who study mental illness and addiction, impulsive behavior — the tendency to act or react with little thought — has emerged as an all-purpose plague.
In recent years, studies have linked impulsiveness to higher risks of smoking, drinking and drug abuse. People who attempt suicide score highly on measures of impulsivity, as do adolescents with eating problems. Aggression, compulsive gambling, severe personality disorders and attention deficit problems are all associated with high impulsiveness, a problem that affects an estimated 9 percent of Americans, according to a nationwide mental health survey completed last year.
Now researchers have begun to resolve the contrary nature of impulsivity, identifying the elements that distinguish benign experimentation from self-destructive acts. The latest work, in brain research and psychological studies, helps explain how impulsive tendencies develop and when they can lead people astray. A potent combination of genes and emotionally disorienting early experiences puts people at high risk, as do some very familiar personal instincts.
"What we're seeing now," said Charles S. Carver, a psychologist at the University of Miami in Coral Gables, Fla., "is a rapid convergence of evidence indicating that when the prefrontal cortical areas of the brain, the brain's supervisory management system, are not functioning well, this interferes with deliberative behavior, and the consequences are often unpleasant."
Few experts dispute that impulsiveness pays off in some situations and, perhaps, had evolutionary benefits. When life is short and dangerous, and resources are scarce, there is a premium on quick response. In studies of baboons and monkeys, researchers have found that animals that are impulsive as adolescents often become dominant as adults, when they moderate their confrontational urges.
In humans, impulsive behavior typically peaks in adolescence, when the prefrontal areas of the brain continue to develop, or soon after, in the young adult years, when it is culturally expected that people will test their limits, psychologists have found.
Yet new research suggests that a taste for danger or conflict is not enough to produce persistent, ruinous impulsivity.
In a study published online last month in The Journal of Psychiatric Research, Janine D. Flory, a psychologist at the Mount Sinai School of Medicine in Manhattan, led a team of investigators who studied 351 healthy adults and 70 others with impulse-related disorders like antisocial and borderline personality disorders. The participants took a battery of tests to measure inhibition, appetite for risk and the inclination to plan.
Analyzing the responses to questions intended to gauge thrill seeking like, "I like to explore a strange city or section of town by myself, even if it means getting lost," and, "I like to try foods I've never tried before," the researchers found that an appetite for risk was associated with smoking in both groups.
But in the healthy volunteers, the appetite was also associated with higher education. In previous studies, healthy risk seekers scored highly for curiosity and openness to new experiences. On measurements of instinctive planning — "I am better at saving money than most people" and "I hate to make decisions based on first impressions"— the researchers found that less deliberative habits were related to heavy drinking in the healthy group and the troubled group.
In cases with personality disorders, deficits in planning were also associated with a history of suicide attempts. The combination of sensation seeking and lack of deliberation characterizes millions of healthy people but appears to be extreme in those whose impulsivity leads to chronic trouble or mental illness, Dr. Flory said.
"The way I think of it is that one factor has to do with the urges people have, and the other has to do with the brakes they apply," she said.
How and when people apply the brakes is crucial to distinguishing those who can flirt with regular heroin or cocaine use while finishing an Ivy League degree and those who die trying.
The people who can binge, gamble or try hard drugs and get away with it have a native cunning when it comes to risk, this and other studies suggest. They are prepared for the dangers like a mountain climber or they sample risk, in effect, by semiconsciously hedging their behavior — sipping their cocktails slowly, inhaling partly or keeping one toe on the cliff's edge, poised for retreat.
"These are highly self-directed people," said C. Robert Cloninger, a professor of psychiatry and genetics at Washington University in St. Louis and author of "Feeling Good: The Science of Well-Being." "They have goals and are resourceful in pursuing them."
Those who are upended by their own impulses, by contrast, are more likely to trust their first impressions implicitly and absolutely, the studies suggest.
"I am a very intuitive person, I can tell very quickly when someone's lying to me, when they're telling a shaggy-dog story," said Thomas Crepeau, 55, a computer systems analyst in Washington who said his impulsive temper helped worsen a contentious marriage.
Mr. Crepeau, who has since benefited from therapy, said he used to act on his hunches immediately. "Other people might allow me 20 words before cutting in, but I would allow them four," he said. "I never had the patience to just wait it out and see if the other person was wrong."
This difference in ability to hedge or self-regulate is partly based in genetic variation, experts say. In a study published in March, investigators at the National Institute of Mental Health took blood samples from 142 healthy volunteers and analyzed a gene called MAOA. The gene directs the body to produce an enzyme that reduces the activity of a brain chemical called serotonin, which strongly influences mood. Earlier studies have linked variations in this gene to impulsive aggression.
The researchers conducted M.R.I. scans on participants' brains while they were performing tasks intended to measure impulse control. In one of the tests, the participants watched as a computer screen presented a series of arrows, boxes and X's, three at a time, as a slot machine does.
The patterns appeared in quick succession, and the participants were instructed to hit a button indicating which way the arrow was pointing. They also had to restrain from hitting the button when one particular pattern appeared. Their mistakes provided a measure of how well they could restrain their reflexes.
The researchers found that, during the computer game, men who had one common MAOA variant, known as the "high-risk" variant, showed significantly less activation than peers with the "low risk" version of the gene in an area called the dorsal anterior cingulate. The cingulate is part of the brain's prefrontal area — its supervisory manager — which is involved in shaping deliberate behavior, in measuring a proper response or reflex.
The participants in the study with the high-risk gene also had deficits in areas of the brain involved in moderating emotion, supporting many earlier studies finding similar gene-related differences.
"On the one hand, these deficits in emotional regulation set people up for strong emotional reactions early in life and make them more vulnerable to trauma, we believe," said Dr. Andreas Meyer-Lindenberg, the study's lead author. "On the other hand, the deficit in cognitive, inhibitory function creates a propensity to act on those emotions later in life."
And life never stops testing those supervisory mental skills. Drug use weakens deliberative regulating skills quickly and cumulatively over time. Coping with periods of extreme stress at any age — starting a new job, breaking up with a romantic partner, recovering from a car accident — can overload the prefrontal regions, leaving fewer resources available to manage emotions, Dr. Carver said.
One reason true impulsivity has been difficult to capture in the lab, said Dr. Martha Farrah, director of the Center for Cognitive Neuroscience at the University of Pennsylvania, is precisely because "it is most manifest in these very high-stakes situations, when people are trying to get what they want, to stay focused, maybe trying to kick a drug habit." And that is when they break down.
None of which is to deny the power of early psychological wounds, regardless of genetic makeup.
People with borderline personality disorder, for example, an enigmatic condition characterized by neediness, emotional reactions and self-destructive behavior like self-mutilation, often misread others' motives and are savagely impulsive in response. "The impulsive behavior always has specific meanings for them," said Dr. Glen Gabbard, a psychiatrist at the Baylor College of Medicine in Houston.
One of his patients, he said, recently called her boyfriend at work, who told her he couldn't talk just then, he was swamped. She took that to mean that he was about to dump her.
"She called him back immediately after hanging up and broke up with him on the spot, as a pre-emptive strike," Dr. Gabbard said.
For her and many others, he said: "It is the psychological meaning of the event that matters most, and for her it was abandonment. Her own father left the family when she was 4 years old, and she sees abandonment everywhere."
In Mr. Crepeau's case, he enrolled in a "compassion power" group-therapy workshop and learned that his contentious nature grew in part out of a history of being dismissed and ignored. Once he understood how this history shaped his impulsiveness, he was able to begin delaying his reactions.
Mr. Crepeau now teaches workshops that help people deal with impulsivity and other relationship problems. In a recent class, he had to contain himself when one of the workshop attendees, asked to present a homework assignment, took the opportunity to brag at length about his accomplishments.
"I couldn't believe this guy; not long ago I would have stepped in" and told him off, Mr. Crepeau said. "But I just waited, and politely told him he needed to do the assignment over."