为什么青少年的大脑总在教唆他们伤害自己？
The Self-Harming Brain
New research looks at the neurobiology of self-harm in teens.
By Terri Apter Ph.D.
Inflicting damage to the body, deliberately, defies every instinct for survival. Yet self-harm is common (an estimated 8 to 30 percent) among teens.[1] The actual damage to body tissue is often minor, but concerns about self-harm extend far beyond the injury itself. Parents feel anxious, hurt, and confused to see a daughter or son, in whom they have invested so much of their physical care, willfully damage the body that they are primed to protect. Psychologists are concerned for the long-lasting effects, for self-harm is associated with a higher risk of suicide and anxiety disorders in adulthood.
According to the standard criteria, self-harm is diagnosed when “in the last year, the individual has on five or more days, engaged in intentional self-inflicted damage to the surface of his or her body for purposes not socially sanctioned.” This then rules out the piercings and tattooing that are painful, or the scarring that in some societies is socially sanctioned. While self-harm is sometimes viewed as a step towards suicide, it often bears no relation to any suicidal intent. In fact, the typical age of onset is 13 years, three years before teens are likely even to think about suicide.
What feelings and thoughts are associated with self-harm? Self-harm was once thought to be a response to stress. But saliva samples show that the stress hormone cortisol is lower in self-harming teens, just as (though this is not so surprising) their pain threshold is higher in standard pain-threshold tests monitoring, for example, the length of time they can immerse a hand in ice-cold water.
At a recent conference on teen suicide and self-harm, Christian Schmahl presented his team’s research on the neurobiology of self-harm. Schmahl showed that self-harming teens have distinctive brain and physiological activity in response to pain and to the sight of blood. Most teens feel terrible when they experience physical pain and when they look at any wound. Their pain intensifies sadness, anger, and frustration. Many adults have a similar response: We stub a toe or bang our head, and suddenly the day’s unfinished business all comes together in a loud “ouch” of anger and frustration. But teens who self-harm experience something different.
Teens who self-harm are calmed by pain. Anger, sadness, and frustration disappear when the teen takes the knife to his thigh or presses the hot match to her inner arm. Relief floods them, and in the wake of pain they are happier, more content and satisfied. The primary motive for self-harm is emotional regulation. The neuroscience behind this has been a mystery, until now.
Teens, with their quick-firing emotions, sometimes try out bizarre techniques for emotion management. Many may try self-harm in a fit of pique, but do not become, clinically speaking, self-harmers because the injury they inflict has no positive effect. Those who go on to be self-harmers find that pain and the sight of blood lower the activity in the amygdala, where the brain locates the rawest, reactive feelings.
This neurobiological model might suggest that the distinctive brain response, being calmed by pain and the visual aspect of injury, is the underlying cause of self-harm. This would have the upside of assuring the teen and the parent that this is not “sick, bad, attention-seeking” behavior, but a problem with an individual teen’s neurobiological responses. This model, however, would have a downside: Removing self-harming behavior from an emotional context would seem to put it beyond the reach of therapeutic treatment.
Our neurobiology and our thoughts and feelings are intricately connected. When we describe neural activity we are not explaining but exploring thoughts and emotions. It is likely that certain kinds of distress or self-loathing or the belief that one deserves punishment produce a context in which pain and injury produce relief.
Finally, I got my comeuppance.
But another clue, Schmahl suggests, might be in that strange discovery that self-harming teens have lower levels of stress. The stress hormone cortisol is usually thought to be bad for us. But it provides a sense of drive and excitement. It keeps us alert and interested. When cortisol levels are low, we can feel sluggish and detached. Perhaps self-harming teens are in search of normal levels of cortisol.
Cortisol normally kicks in at various times of the day, particularly in the morning. When levels are high, the body’s own homeostatic cycle comes into play, and the cortisol levels are dampened by a built-in soothing effect. The suppressed cortisol level in teens who self-harm disturbs this homeostatic cycle. Lacking both the normal level of cortisol and its calming counterpart, they raise cortisol level by self-harming, which they also use to dampen bad feelings. What self-harming teens may need is more, not less, stress in the form of stimulation and drive.
The good news is that when teens cease to self-harm, either as a result of therapy or maturity, their neurobiological responses return to normal. Their reaction to pain is no longer blunted. They no longer feel a compulsion to self-harm when they are sad or lonely or frustrated. They are no longer soothed by the sight of their own blood.
We can learn a lot from the self-harming brain. Rather than fear that its idiosyncrasies are permanent, neurobiology may point the way to more effective therapies.